Sounds to me like you have a firewall blocking the connection, can you disable mcafee briefly to see if thats doing it?
See if you can ping one machine from the other... open the run box and type cmd, then type ping xxx.xxx.x.x where the x's are the ip of your second machine.
You say your laptop is wireless, does it connect to a WAP on the router or a wireless card in the desktop?
Intel core I7 920
6GB OCZ platinum 1600
Samsung 1TB F1 Spinpoint
Samsung SM2443BW 24"