Does le server have to run Windows 2003 Server, ou will Windows XP Professional work?
Yes, Windows Server is required.
Where do I download le WSUS packages from?
Microsoft's website: WSUS 3.0
How can I configure mon computers to cherchez updates depuis mon server à la place of le internet?
Il y a a deployment guide & a step-by-step guide that explains it tous in detail. The executive summary is:
If votre computers are members of a domain, alors you can use group policy.
If votre computers are stand alone, alors you will have to modify le registry of chaque machine. THis KB covers les deux scenarios.