Trouble leaving Windows behind.....

I've just got a new iMac (and fantastic it is too...) - why I took so long to take the plunge is beyond me.
Problem is that I still have to use a PC for some software until I can afford to upgrade to mac versions, so can't ditch the PC yet.
I've turned on file sharing on all sides (still using the Windows wireless network for the PC).
I can "see" shared drives available on the network on the PC from the Mac but cannot see any of the Mac drives on the network from the PC (I have one formatted macintosh and one formatted FAT32).

Am I attempting to achieve the impossible?

nope, I have a mixed network that plays quite nicely.

File sharing between Mac and PC

should help, but this is actually a frequently encountered problem, so there are a bunch of helpful threads around as well