Which browser are you using to access SPS from the Macs?
We have 2-300 Mac users on our network as well, which poses a problem in Sharepoint. I've found that the best browser for us (subjective) has been Camino v1.0. There is no office integration of course, but we can access sites. Safari doesn't seem to work at all, and IE doesn't work well (and is no longer being developed, I believe).
Other than that, we are looking at a solution down the road that involves RDC & terminal services, Citrix, or possibly an Apple virtual PC environment on each Mac (thanks, Heather).