Has anyone else had this problem?

On virtually all of our Windows XP computers, a network drive mapped to a
windows share will time out after idle for about 15 minutes, at which
point trying to access the drive will result in a loooong delay (15-20
seconds) before folder information again becomes available, after which
they behave normally. Netware drives work fine. All affected PCs are
Windows XP SP2 with Novell Client 4.91 SP3; all PCs of this configuration
are affected.

Things I have already determined:

1. Client 4.91 (no SP) does not exhibit this behavior.
2. Only shares to XP and 2003 shares exhibit the delay
3. 2000 PCs mapped to the same shares do not have this problem.
5. Even 2000 machines with the exact same version of Novell Client!
6. Changing the network provider order doesn't do anything.
7. Changing the timeout value for MUP does nothing.
8. Manually adding a reg value for KeepConn and AutoDisconnect in the
Parameters section of the Lanmanworkstation doesn't do anything.
9. Changing similar timeout values in the Lanmanserver service on the PCs
(and servers) on which were located the shares also did not help.
10. All patches were applied to the client, in turn, to no avail.
11. It is not a DNS problem, and doesn't apear to be a name resolution
problem of any kind.
12. Uninstalling the Novell Client removes the problem completely, but
this is not a particularly useful solution.
13. Uninstalling essentially useless portions of the Netware Client
(middle tier, security stuff, iPrint) has no effect.
14. I am losing my mind.
15. A packet trace run during one of the delays shows the *client*
prompting the *server* for trust authentication (SMB_NETL protocol, "SAM
LOGON request from client") which goes unanswered, takes five seconds to
**** out, and is repeated three times (roughly five seconds). THIS IS THE
DELAY. But what is this? And why does it only happen when Novell Client
is installed?!

Any suggestions for a fix? Workaround? Correct procedure for seppuku?