I take it your wireless connection is working. i.e. you can ping each computer from different machines? to do this on the first computer go start, run, cmd, ipconfig.
note down the ip address example 192.168.1.1
go to the other computer and do the same thing, then from the second computer go start, run, cmd, ping 192.168.1.1 or the actual ip address you have.
if you get reply then your connection looks good, as described above just right click the folder you want to share and select sharing and security.
Not the c drive as this can be a security issue.
Hope this helps
Capdan