Can i have more than one domain installed on a w2k professional ?? in other words, i want to be a part of two networks, and would want to choose while signing on.

You could if the domain is a child domain. If your enterprise has multiple domains you can click the down arrow and select any of the trusted domains. If the other domain is completely separate and no trust is established between them, then no, you can't. There may be third party tools that allow something like that though.

There is another way. You can login to one network, and then setup a VPN (Virtual-Private-Network) to the other, as long as you can have a direct link to both at the same time. However, from memory of when I was using a network with a VPN, you can only browse/utilise one of the networks at a time, but it doesnt require you to log-out or anyhing, only locks network access between the two. There should be a way around it, but it may be a risk to network security.