7 ultimate wont share a printer, credentials

Hello

I'm the owner of a PC repair shop and I've got an important client trying to share his USB printer (brother mfc) from a 7 pro desktop at his house.

1. Mark-PC (running 7 Home) -- hosts the printer
2. Mark-Laptop (Vista Home Prem.) -- Sees printer and prints ok (I suspect because user and password are identical across both machines)
3. Emmet-laptop (Vista Home Prem.) -- Sees, and adds printer, enter credentials... can't print, job times out saying access denied
4. Owen-laptop (Vista Home Prem) -- sees, adds printer, can't print. Error jobs say access denied for job status when you right-click and hit properties
5. Wife-Desktop (Windows XP pro sp3) -- haven't looked at this one yet.

On Mark-Laptop I started by going
Devices and Printers
Right Click
Run as Administrator
Add Printer
Network Printer
"The Network Printer I want isn't found" [button]
Type in Printer name by share name: [field]
\\Mark-PC\Brother MFC 7420

Type in Credentials:
User: Mark
Pass: sell

Added the printer, it prints, no problem. rebooted, still prints.

On other laptops without the "Mark" user, you type in mark's user/pass credentials [x] remember these credentials... and it adds the printer and prints the test page. But after logging off/on it stops working, producing access denied errors on print jobs.

Network is a workgroup called "Workgroup", and on seven, the net type is set to 'Home.' Sharing is activated on the printer, also discovery, print and file sharing, 128-bit all turned on, which explains why his laptop works.

Unfortunately for the other two vista laptops.. When I try setting permissions on the printer from the seven machine, I try to resolve user names on the workgroup, but only the "Mark-PC" location shows up, NOTHING network related can be seen from available locations. is that normal??