I don't use Win's Homegroup. Both of my PC's (each dual-boot, WinXP Pro and Win7 Pro) are simply using the old-fashioned original "workgroup"... just as they always did when I was only using WinXP.
Just right-click on Computer, select Properties, and go down to the computer name, domain and workgroup settings area, and click on "change settings" to get the old-fashioned familiar "System Properties" dialog with the famliar "Computer Name" tab.
Your full computer name should be shown there as well as the "workgroup" name that machine belongs to. You should push the "change" button to either rename your computer or change its workgroup. I've not used the "Network ID" button to trigger the wizard to join a domain or workgroup... never had to, probably because I entered both the computer name and workgroup name at the time when Win7 was being installed and I came to that prompt (on both machines).
While there may be some new functionality available with "homegroup" I don't know what that might be nor do I care. I just wanted to be able to get to all partitions (and thus all content, via "full access" in permissions) on either machine from either machine, no matter whether either machine was booted to WinXP or Win7 at the time.
This is 100% provided through "workgroup" and it's available in Win7, and works exactly under Win7 as it did under WinXP... so why not just still use it (I argued with myself)? Hence my decision to just use old-fashioned "workgroup" and be done with it.
And I have 100% of my objectives satisfied. Everything from every partition on either machine is "full-access" available to either machine, no matter where I'm sitting and no matter which OS I'm booted to there at the time. I also have full access to either of my two printers (each one USB-hosted as "shared" by the machine to which it is connected) from either machine, again, 100% exactly as it was when purely under WinXP with "workgroup".
Yes... there is that mystical "homegroup password" that gets generated at Win7 install time that you're supposed to write down, but can be re-obtained after installation if you have another machine that wants to be part of the same homegroup (they all must enter the same password, I think). But why get involved at all??? Ordinary simple old-fashioned "workgroup" still is available and still works perfectly to provide exactly what I am looking for.