The switch really shouldn't be too awful. Drivers support is exponentially better than XP. Most hardware will probably work immediately after install. However, you'll definitely want to get the latest driver from nVidia or ATI.
If anything, I hope you have another hard drive or partition to back up whatever files you want to keep since you're going to have to completely format the disk (there's no upgrade option between XP and 7).
As far as applications go, I really haven't found anything major that I could use on XP that I can't run on 7. I was a bit disappointed that a couple utilities like Hyper-Terminal and telnet are now not included but that really isnt an issue for most users. Even if it were, it's nothing that PuTTY doesn't do.