The Islamic Republic of Iran is on the road of becoming a major regional player in the region, let there be no doubt about that. I think it is very apparent since the day that President Amadinejad and his hardline Conservatives were elected to office (more or less if you discount the fact that Reformist candidates were barred altogether), that Iran has adopted a more bellicose posture in the region.
Let me make it clear though. This approach is one that is pursued by the incumbent administration in Tehran, it is not shared by the people of Iran nor by the Reformist opposition, who prefer dialog and diplomacy with Iran's neighbors. So yes it is very true that Amadinejad, (who has a background of a hard line Revolutionary Guard) has made it a habit to not only to equate the development of Iran's nuclear program with national self determination, but also to overtly or covertly support resistance movements and rebels in some countries of the region.
I think no can argue that, Hizbollah (the Lebanese based Shiite led movement by Sheik Nasrallah) or the Shiite rebels in Iraq are strong enough to stand their ground and launch attacks on their own either against Israel or US occupation forces in Iraq, if not for the substantial financial logistical diplomatic and moral support they receive directly from Tehran. The regime in Tehran is as hypocritical as the one currently occupying the White House, since both are religiously inclined and obsessed with using lies and propaganda for manipulating public opinion and domestic consumption. On the one hand Amadinejad claims to want nothing but peace and security in the region , while on the other and in reality they cannot refrain from interfering in the affairs of Lebanon or Iraq. This is something they always accuse America of doing, which yes America does, but they do exactly the same thing hoping it will pay of political dividends.
Looking back I do not consider the 34 day war between Israel and Hizbollah as an incident that really benefited Iran, even though Hizbollah's reputation and standing among Lebanese and Iranian Shiites soared thereafter ( bear in mind Hizbollah which US has identified as a terrorist organization is seen by devout Iranian and Lebanese Shiites as a liberation movement that also provides extensive social and welfare services to Lebanese citizens). The ayatollahs in Tehran may have had reason to celebrate Hizbollah's successful defiance against Israel ( Iran's arch foe) , but overall it is clear that Lebanon has been the ultimate looser, and it emerged much weaker than ever before from that conflict. Years of recovery have been brought to halt and old sectarian communal divisions along religious lines ( 50 % Lebanese are Christians, rest Muslims, Druze) have re-emerged. No doubt that Israel also had a considerable role in weakening and deliberately damaging Lebanon and its infrastructure through the proxy war.
In Iraq, the Amadinejad government has not shied away from opportunities to arm and support the Shiite insurgents who fight against American troops. Officially they claim that it is America's presence that is causing the rebellion in Southern Iraq. Yes to a large degree it is true that Bush's misguided incompetent Iraq policy has caused this,but Tehran is adding fuel to the fire by directly supporting the rebels. In my mind there is no doubt that for propaganda reasons and for domestic consumption it benefits the Islamic regime to have America bogged down in Iraq and to create an image that shows that instability stems from that alone. Of course the aim of this also entails to draw the weak Shiite led Iraqi government much closer into Iran's orbit, with a prospect of making or turning Iraq into Iran's Shiite client. Contrary to official comments, I think Iran would be very happy to see Iraq 's instability continue rather then it ends.
As regards the remainder of the Middle East, I think it is really difficult to claim that Iran is funneling money and support towards rebels or trying to sabotage pro American regimes. The ayatollahs are not that stupid. They know that beyond extending the sphere of Shiite influence in the region, there is not much else they can do. Bear mind that the ayatollahs strongly dislike Sunni based resistance movements (like the ones in North Africa or Middle East) , they also harbor no love for the resurgent Taleban in Afghanistan ( the ayatollahs consider them to be way too backward even by their own religious and moral standards) nor do they like militant Al Quaida ( which aims to overthrow secular authoritarian - US-Israel friendly regimes in the region). In fact Al-Quaida officials have been captured on Iranian territory and are languishing in Iranian prisons, awaiting their death.
The ayatollahs are smart enough to know that the power of emulation of ideas can extend Iran's reach in the region much faster and securely than anything else. And by that I mean their defiant pursuit of a nuclear program against the odds of US or Israeli military intervention. Others in the region, given the continued success of this defiant strategy, may also feel embolden to implement policies that run counter to Israel's and America's regional wishes or interests. That is the real threat, the threat of ideas that Tehran is exporting around the Middle East.
It is quite likely that Iran's foreign policy, beyond extending bilateral relations with Muslim and non Muslim countries, will be more assertive, with former hard line Revolutionary Guards regaining and taking up positions in government, and competing for power with more moderate clerics and moderate reformists technocrats.
This presents a real challenge to the ruling Iranian establishment. It could mean for instance greater support for Hizbollah and more support for radical Shiites in Iraq, and not less. It is very unlikely that a reformist government (bent on diplomacy and accommodation) will come to power in the next few years, so we can expect more assertiveness and defiant if not bellicose rhetoric coming from Tehran.
The real dilemma in all of this, is that the Iranian people are not supportive but rather highly appalled by this Islamic regime. They wish it was eliminated from the face of the earth. This in turn would allow for a democratic secular Iranian government to emerge that really reflects what Iranians ( who are mainly secular) want: secular democracy, peace, social security, jobs, education and good relations with the West, esp USA.