I would recommend you didn't upgrade to 2.5

If you don't know how to get the necessary libraries to run the new graphical config tool (or indeed know how to run the non-graphical config tool), then you probably don't want to be messing with 2.5.

If you must run 2.5, do it on a separate disc (or machine) where you have *no* data that you remotely care about, and on a machine you don't mind crashing, failing to boot etc. Don't mount any local discs you care about read-write.

2.5 is the unstable series. Currently it's passed its feature freeze, so theoretically it should be more stable now. I've built a few 2.5 kernels so far - about 50% didn't build and a few of the ones that didn't build didn't boot.

In answer to your original question: you probably need to install the libqt2-devel package from your original distribution. Or it might be a later version. Or something. Anyway it should be included on your current distro if it's vaguely recent. If your current distro is out of date, don't attempt to build or install 2.5 as it may not work anyway.