try this
yes possibly your firewall, however you can bypass the workgroup, go to your desktop comp, go to command prompt type ipconfig and get the local ip or manualy do it from your tcp/ip protocol:
example comp1(desktop): 10.0.0.1 laptop is 10.0.0.2, from your laptop go to run and type \\10.0.0.1\ (then press enter or whatever)
if nothing works and you know you dont have a firewall running go to control panel -> admin tools-> services: then make sure network connections is started, i have worked on manufactured pcs w/ wiindows Xp, that disable these settings such as dell