I've been seeing a lot of questions about this and people struggling with getting their packages to work in VS 2008 that were developed in 2005.
For most packages, it should just work. However, there are some gotchas which you need to be aware of. I've been working with our UE team on beefing up our documentation in this area but for now, here are some links to documentation that will help you migrate from VS 2005 to VS 2008:
We're aiming to add more to the official docs on MSDN so keep an eye on it. Specifically, in VS 2008, the experimental hive no longer writes to HKLM. Since we write to HKCU, if you log in as a different user, you'll need to recreate the experiemental hive.
If you run into any other migration issues that we don't have documented, feel free to contact me.