|can a person login in a domain with only 1 computer?|
Do you mean, can you restrict a domain user to only logging in on one machine? If you do, the answer is yes
how to block internet in xp? leaving some sites
Hmmm............3's party software for restricting internet access.
can domain users see workgroup?
You could allow a PC or laptop to be able to login to both a domain, or a workgroup by using separate hardware profiles and choosing the appropriate one depending on what they're connecting to at that moment in time.
Alternatively, there is 3'd party software that you can use to change your TCP/IP settings and domain/workgroup access on a single PC/laptop. You can't do both at the same time though unless the PC in question has dual NIC's.