Laptop HD upgrade questions

[akaSM]

Hi, I got my laptop about 2 years ago because my desktop sucks at running games of college, and since it doesn't suck at running games AND Steam's offers are quite nice, my hard disk is filling up. I want to get a new hard disk for it.

Basically, I know nothing of laptops HDs (size, whatever) and I'd like some help, speciffically:

• Does this thing need a 2.5" HD?
• What's a reliable HD brand?
• Where can I get the HD? (pages with worldwide shipping)
• Anything I could've missed related to this

My laptop is a Dell Studio XPS 16 (1640)

Yeah, I've messed with other stuff before so, I think I can handle this one. I've opened my PC, got a second HD in it, reused and old CD drive and so on. Also, I've opened stuff for the funsies (phones, watches and several other stuff lying in my room), and so far, there have been no casualties