Forget about Scrum, XP, and all the buzz words. Let me introduce a new buzz word.
Start with demonstration-based agile (DBA) on a small scale. With demonstration-based agile, you insist on only one thing:
Regular Demos. The development staff demos the product to the product manager and other members of the team at the end of every week (or some other short period).It's a lot easier for a team to agree to regular demos than it is to short iterations or frequent releases. Yet regular demos aren't much different. The team must iterate on developing the product and must have something to "release" (as a demo) frequently. Regular demos also stimulate frequent communication. Finally, the team sort of plans "tests" by defining in advance what to expect from each demo.
Some curmudgeons may resist the idea of regular demos, but for many the concept is easier to swallow than all of the agile practices that fall out of it.