Mac OS X doesnt use Bonjour to file shares with Windows it uses SMB (samba).
make sure file sharing is enabled in Sharing preferences and "Share files and folders using SMB" is ticked & your username is ticked in Options. also make sure your PC's workgroup name i.e. WORKGROUP or MSHOME is entered into "Workgroup" under "WINS" in the advanced network preferences. easiest way to get to this is type "wins" in System Preference's search and press enter. then make sure file sharing is enabled in Window's firewall.
Your PC should appear under "Shared". to "see" your Mac open My Network Places, click "View workgroup computers" under Network Tasks, double click your Mac's name and then provide your password. this is assuming your using XP, i dont know how to do it in Vista.