For uni, get 1gig (usually 2x512) of RAM, a non-generic brand. Large calculations (or mistakes, in my case) in Excel tend to use up a lot of RAM and you never "only" have Excel open..
A Sony case will be expensive? (I can't see Sony having cheap anythings) If you're feeling adventurous get your own case (anything from $50-$200+) and then get him to install everything in it. Having an ugly case sucks
It's also a good idea to remind him that if your case is black, you want BLACK EVERYTHING. That is, black CD/DVD-RW, black 3.5" drive (if you have one), black keyboard/mouse, black monitor. Nothing uglier than a beige drive in a black case
DVD Burners tend to be pretty much the same, just make sure it's 16x dual layer (best at the moment I think). Lite-on, Pioneer, Sony, you're just paying for the brand.
I find my brand spankin' new Logitech MX Wireless Duo to be awesome muchly - the navigator set is also good.. MS tends to be more expensive though so if it doesn't make a difference for you get the MS one. Try to get an ergonomic mouse unless you're left handed because much-clicking can be bad for ze ol' RSI.
XP home is fine if you're just going to be using it for general purposes. If you have a wireless network make sure you get SP2 (you can download it but it might be nice to get someone else to do all those updates for you) as well.
Also a good monitor is more important than good speakers. You can't go deaf with bad speakers but you can go blind with a bad monitor. They're pretty cheap now (even LCDs) so it shouldn't push your budget out too far.