'Access computer from another network' security Setting resets its

I have networked 4 PCs through a hub. 1 is XP Pro (with SP2) and the others
are running 98. I had the usual problem of being able to access the XP
computer throught the 98 workstations - it kept asking for password for
\\computer\IPC$. I read numerous troubleshooting postings and eventually
managed to rectify the problem with the following:
-enabling guest account
-setting network policy from guest to control
-logging onto the network on the 98 machines using same user names and p/w
as on XP machine
-ensuring nothing is set for the 'deny access to this computer from the
network' policy
-setting the 'access this computer from the network' policy to 'everyone' or
to specific users
Having done all this it worked just fine and I could access the hard disk of
the XP comp from the 98 comps. However, a few minutes later it stopped
working - I couldn't access XP machine from 98 comps, but could still access
98 comps through XP machine. On investigation of settings I found that the
'Access this computer from the network' policy setting was blank- it had
reset itself. I set it again to 'Everyone', clicked apply, and it works. A
bit later it clicks off again- I open the Local Security Settings again and
the policy is blank. Other policies I have changed have kept their settings.
It seems like something is overriding this setting and changing it back
again.
I have simple file sharing.
Would much appreciate any suggestions as I hope to use XP comp hard drive as
a central hard-disk for network?
Nick