Use workgroup, not homegroup, if you want dependable easy-to-understand networking of your home computers, and full access to all drives/folders on any machine from any other machine, which works for both WinXP and Windows 7 machines.
Make sure each machine (be they Windows 7 or WinXP) specifies (a) a unique "computer name", and (b) the same "workgroup name". You just need one "workgroup name" which you can invent yourself, but it needs to be specified the same on each machine.
For full unrestricted access to any drive on any machine from any machine, make sure each drive on each machine is (a) shared (at that top drive level), with (b) "full control" given to a user named "everybody" in permissions. You will need to ADD a user named "everybody" and then push the "permissions" button and check "full control".
With all machines on the same workgroup, and all drives on all machines "shared" and with "full control" granted to "everybody", every drive/folder/file on any machine will be (a) visible and (b) accessible from any other machine. You will never hear a peep from Windows, except perhaps the very first time you access another drive when possibly a userid/password "log in" may be asked for, in which case if you check the "remember" box you'll never hear from it again. I avoid even that problem by using the same username/password on all of my machines in my home network.
If you have (or want) "shared USB printers" (i.e. locally connected/hosted by one machine via USB cable to that machine, and defined as "shared"on that machine) and all of your computers are 64-bit or all are 32-bit, it's trivial to use the ADD NEW PRINTER dialog to "connect" to that network-available shared printer object from anyother machine. It only gets more complicated (but hardly difficult) if you have a mix of 32-bit and 64-bit host/clients, and then you have to get the proper driver
available to each machine.