Sure. I have basically that setup running here (Dual G4 Powermac instead of iMac). This assumes Mac OS 10.3.X. I'm also assuming you have a wireless access point and router-based LAN (can't help you with an ad-hoc wireless LAN - but someone else might be able to).
Finally, the Mac needs to be sent a Postscript job from the PC; I don't know how to "fake" a postscript job if the driver isn't a postscript driver. (Note that the printer doesn't need to be a postscript printer; the BSD subsystem on the Mac converts the postscript job to the correct output for the printer.) Basically, see if you can get it to work; if it doesn't you may need to ask the question on a Mac site.
0) Download the latest windows printer driver from the printer manufacturer's site onto your PC. If you have a choice, select the "postscript" driver.
1) On the PC: Start -> Settings -> Control Panel -> Administrative Tools -> Local Security Policy.
2) In the window that pops up, open the + next to "Local Policies", then click on "Network Security: LAN Manager authentication level", ensure it says "Send LM & NTLM - use NTLMv2 session security if negotiated". (These 2 steps are necessary to set the SMB security to a version compatible with the Mac's SMB implementation.)
3) On the Mac, open "System Preferences" from the dock (if it isn't there, try /Applications/System Preferences)
4) Click the "Sharing" pref pane icon.
5) Click the lock to authenticate (the account must have Admin privileges), enter your account's regular login password.
6) Ensure the boxes next to "Windows Sharing" (enables SMB), and "Printer Sharing" are checked.
7) Back to the PC: Start -> Settings -> Printer & Faxes. Click the "Add New Printer" task or icon.
8) Hit next to clear the intro screen
9) On "Local or Network Printer" page, click on "A network printer, or a printer attached to another computer". Hit "Next".
10) On "Specify a Printer", click on "Connect to this printer (or to browse for a printer, select this option and click Next)". In the "Name" box, type (without hitting enter at the end):
\\[mac's ip address in xxx.xxx.xxx.xxx form]\
A popup completion menu should appear with all the printers attached to the Mac. Select the printer, and hit "Next".
11) Windows may or may not find the right driver. If not, click "Have Disk" and browse to the location where you downloaded the printer driver (in step 0) and hit "next".
12) Windows will install the driver, then ask you whether you want to make it default. Answer as desired.
13) You should see a printer in the Printers and Faxes folder now. Right click, hit
"Properties", and try printing a test page.
Sorta straightforward, sorta.