|First off, wrong forum, this is not a hardware question. Workgroups have no effect on the ability to share files across them. If you have more than 10 computers, I highly recommend that you invest in a Windows Server. Servers running SBS essentials are good for beginners. Now, down to answering your question:|
Take note of either the computer name or the IP address of the computer sharing the file. Usernames and passwords on the computer hosting the file need to match the ones on the computer trying to access the file (eg. Username John and Password Cats123 need to be on both the host and the client). Don't worry about which workgroup each computer is in, that only matters for browsing in My Network Places. You can access any computer from any other computer by using UNC addresses (\\johnscomputer or \\192.168.1.50). I hope all of this helps. If you still are having trouble, I'll look for a basic workgroup networking guide for you.
BL Technical Services
IT Support Maryland