Can't get 3rd computer to use common workgroup name

Hi,
Why can't I get my new 3rd computer to retain the "common" WORKGROUP name of
the 2 original computers?

Original set up consisted of: 2 XP computers networked together via router,
then ADSL modem to the Internet. Everything was working fine - file/printer
sharing, Internet access etc. But I recently added a 3rd (XP) computer to
the network and cannot get it to "retain" the custom/original WORKGROUP name
of the other 2 computers.

Ran Network Wizard on new comp 3 -- says "welcome to CUSTOM WORKGROUP". But
after reboot it goes back to default MS workgroup name. Manually changed the
workgroup name on comp 3 to match existing name -- get same welcom to
CUSTOM WORKGROUP -- but, again, after reboot it goes back to default MS
name.

How can I get the new, 3rd computer, to use/retain the original WORKGROUP
name?

If you need anymore info please ask. I'm green to networking more than 2
computers. Any insight is appreciated.
Thanks