Hi,
make sure your basic windows networking "workgroup" matches you other LAN pc's that may not be running Win7...This is different to Win7 Homegroup setting.
Click on SYSTEM icon in control panel (using small icons setting for control panel -- WHat idiot used the name "Small Icons" to set the control panel settings is beyond me)
Under computer name, domain, and workgroup settings is the workgroup item...change it from there to match all your other pc's on your lan.