Install the airport utility for windows.. this is not necessary but helps.
Set the Airport Extreme and all names to SMB compliant.. short, no spaces, pure alphanumeric.
Set the disk sharing workgroup name to WORKGROUP. (assuming you do use defaults).
Turn on the guest account to have read and write access.. again not 100% necessary but helps.. in secure environment you will need to muck around with username and password.
In windows explorer, type \\ipaddress or \\airportname (obviously replacing the placeholder with either the actual ip address or actual airport network name)
If you still have issues tell us.