I think it depends on the reason they became terrorists. The IRA *only* wanted the brits out of Northern Ireland. Al Qaida wants to destroy the west or make us muslims. Usama wants to destroy america altogether.
Negotiations work with IRA types because they want to achieve a political goal and that's all. If they get all that they ask for they'll stop. For that to work with al qaida all of the us government would either have to commit suicide or form a new sharia based government. I don't think america could become islamic enough fast enough, so there's really nothing to negotiate.
:magus:
just in case you think I'm making this up:
http://www.memri.org/bin/articles.cg...had&ID=SP65504
