Again, make sure they are all on the same workgroup. This is found by right clicking on My Computer, Properties and choosing name and looking at the workgroup name and clicking on change if necessary. For WIN7, right click My Computer, Properties and Change Settings. These will all require reboots at least in XP. The workgroup name can be anything only they have to be identical.
Another thing that can be helpful, which is a variation of the above post, is insuring that all your computers have the same username and password.
Go to Control Panel, Homegroup, then Homegroup troubleshooter.
Also, if you have McAfee or Norton ANYTHING, remove and give to chartiy. Or better yet, an enemy.
