Tom,
Don't know if this helps, but you may consider using it as a workaround to your problem.
I had 2 clients having similar problems, Win2k server, Win98 clients in this case. (Each having about 10-25 concurrent users)
What I did in my app was to open all frequently used tables in an invisible form using default data session and do not close them until the user exits from the app.
The initial startup will be slow but all subsequent screens will be lightning fast (<1 sec) as compared to opening tables (under private data session) each time a form is launched. I've encountered (under the old method) it could take almost 20 seconds for a screen to come up when there's more than 1 user. In these cases, the coverage profiler shows that the bottleneck is in the "use tablename" commands.
Now the users need only to wait a bit during system logon but subsequently everything is fast.
HTH
Yau