In Windows 2000 Professional, you can only join a single domain. Thus, you can't log in to one domain one time and another domain another time without actually joining each domain. You can connect to and use the resources on each domain, but you can't browse them.
One solution to the problem is to create a trust relationship between each domain. Also, there are third-party products like NetSwitcher that help you quickly switch between different configurations, but you must evaluate these products to make sure they perform as you expect.
This was first published in February 2003