Darren,
We have a mixed mac/win2k/winxp network. We have less than 15 machines in the office and I did look into the whole samba/win2k domain issue and in the end realised that I really didn't need a domain at all. The network works just fine on a workgroup, and as long as each user logs onto their win2k/winxp machine with the same log/pass as their account on the SME5 box everything works a treat.
All the best,
Julian