How many cpus and cores can I use ?

Microsoft Windows  is licenced by processor socket.

Windows XP Home and Vista Starter and Home Editions support 1 processor.

Windows XP and Vista (except Starter and Home) support 2 processors (single, dual or quad core)

Windows Server 2003 Standard Edition supports up to 4 processors (single, dual or quad core)

Windows Server 2003 Enterprise Edition supports up to 8 processors

Windows Server 2003 Datacentre Edition supports up to 32 processors