About Windows Installer, the .NET Framework, and Visual Studio.
We received our Windows Media Center 2005 from Dell yesterday and I'm quite pleased. Not only is the machine a nice configuration but the capabilities of Media Center are great. There's nothing like kicking back on the home office couch and listening to music selected via remote on your 5.1 surrouned sound system or watching recorded TV in the living room via the Media Center Extender for Xbox over your Wireless-G connection (which is required since B can't carry the bandwidth requirement).
If you get a chance to play with one of these I recommend it. The Best Buy in Bellevue has a couple of nice set ups to try and I imagine other locations and retailers do as well.
The problem is transfering gigabytes of digital photos and other files. Setting up a new machine can be fun (although I admit I didn't start by reformatting this one like I usually do) but copying all the necessary documents, configuration files, etc., can be laborious.
I'm also taking this opportunity to do something I should have long ago: running under LUA, or a least-privileged user account. While I've never actually had any viruses, worms, spyware, etc. infect any of my machines since my first C64, it's always a possibility and not being an administrator means that the machine can't easily be infected. Not trusting anything that touches your computer is always a good idea.