Right... shall we give you some correct answers now! :^)
1) Go to System Preferences, and then go to 'Sharing'
2) Look for 'Windows Sharing', and tick the box to enable it.
3) Click on the Accounts button which should be on the right of that window, and tick the accounts that you want to allow access from Windows. At the bottom of this is the address that you can use on the PC to connect to this computer, make a note of this.
4) Go to Windows Explorer on the PC, choose to 'Map A Network Drive', and enter the address mentioned above. Login with your username and password from the Mac, and you should now have access to the Mac drive.
I KNOW for a fact this works, as I have it setup at the shop here. I have all my admin stuff on the Mac, but I have to use windows for the software to run the shop. So I simply have my Mac drive connected (as above) and I can access the files from the PC.
OH... and yes, you can write to the drive too!! Some people have no idea! :^)