The nice thing about Dell is their support and warranty service - I have a 3 year if anything happens we fix it warranty. If my laptop gets struck by lightning, they replace it. I've gone through six keyboards (very comfortable to type with, but cheaply made!) and a hard drive so far. However, I haven't paid a cent for replacements. When you build your own PC (all of my desktops were built), there are easily ten different vendors you might have to contact. At least you can pick quality parts, though.

I'd really recommend a laptop for school - they're so much easier for, well, everything. The key is getting one that has a touchpad and keyboard you can use comfortably. I loathe the Panasonic Toughbook keyboard/touchpads. They're awful things. My old HP had a very nice touchpad, and I love Dell laptop keyboards. They're nice and comfortable. Pay attention to screen size, resolution (1920x1200 ftw) and battery life, too.

17" models (1920x1200) have an incredibly short battery life. Probably about 1 hour on the standard battery (I believe it's 65 watt-hours). I bought the 85 watt-hour, and it lasts me about 5 hours at half brightness (1680x1050, 15.4"). Also, while Forren loves his 1920x1200, I prefer a ~15" widescreen, mainly because 17" laptops are ungodly large. Also, it's the best combination of battery life and viewspace (imo).

But Forren is right: get one your comfortable with. Also, if you use it for notes (which is the main reason for a laptop in school), make sure you back them up often. Nothing worse than losing all your notes if your hdd dies.