Connecting w2k prof with 3 domains

HI,

I have 25 windows 2000 professional and also i have 3 windows 2000 advanced server with active directory installed.I made 3 domains and the domain names are : 1) shop.com
2) public.om
3) private.com

i have these 3 domains.Now i want my users can login on any domains.How i connect my 25 windows 2000 professional with 3 domains.I want my users can choose domain name from logon dialog box in which domain they want to logon.

I would appreciate if someone provides me the solution.

With regards.

Anurag.