I doubt it matters who planned or supported this attack, it's potentially going to rip the country in two.
Bhutto was a voice a lot of people were hoping could come back to the country and bring some semblance of democracy with her. She had a lot of popular support and a lot of momentum.
The assassination will no doubt provoke angry responses from her supporters. We'll probably see large scale riots over the next few weeks leading up to the elections which Musharraf will use to further legitimize and cement his emergency powers and possibly call off the entire election process for several more months potentially sparking more violence and instability and cementing his rule.
The question of spillover into or from the surrounding region and the US attempts to push Pakistan to be a model for democratic development in the region will be the wildcards. If there is violence, US intervention may be fairly swift (political support/pressure, not direct intervention) but the more the US intervenes the more backlash we may see from within the country.
It's an interesting and potentially scary situation
Fingers crossed for the best
Twill
(oh, and Theognome, go fart somewhere else. Keep the spam and flames out of here. Welcome to CC, shape up or ship out

)