Passwords on computers in two different workgroups?

you want to eat fish and to sit in the boat, I see. If you need these functions, then either it is fair upgrades to XP Pro (win7 pro), or hammering on the conscience of a pirate, either globally change the paradigm in the field of desktop OS. Look how many options you have to choose from.

the guest will disconnect and set on the balls you need someone, user is appropriate.

to fix the registry in one place and home will be pro (if not confused)
and then — standard tools...

setting the NTFS ACL are available in windows xp home in safe mode, so remove "All" the folders/files/drives it is real.
The catch is the lack of winxphome snap-in secpol.msc, where in your case you should change the parameter "Network access: model sharing and security for local accounts" to classic. Can look for a solution to change this setting directly in the registry?
If the balls have access to Everyone and have a folder on drive "system"+"admins"+"Users"(without "All"), using classical models(when asks login+password) must submit a request, although in the case of a home may raise an error(no access to the resource).

[HKEY_LOCAL_MACHINE\\SYSTEM\\CurrentControlSet\\Control\\Lsa]
"forceguest"=dword:00000000
it changes the parameter access model(described above) if such key there — you can try to create it.