My advise is to ditch the 'homegroup' bullcrap in Windows 7. Set the network type to Work instead of Home.
Just add each computer to a normal windows Workgroup by doing this
1) Right click on Computer (aka My Computer)
2) Select Properties
3) left click on Change settings in the Computer Name, domain and workgroup section
4) left click on Change in System Properties tab
5) Select Workgroup, add each machine to the SAME WORKGROUP. I would call it MSHOME or something easy to remember
6) Supposedly you have to reboot each machine after making this change, I recommend it but sometimes you will be able to view the work group without doing so..
Here comes the most important...