Random IPX Network errors is sort of vague- I dont think you need to do anything special for IPX if your only using a 4006 at layer 2. I don't know what SW you're running, I've seen 4006's running SW 5-5-4b not get the Novell login screen. A re-boot seemed to fix the problem. You might try upgrading to SW 5-5-7 if your memory is adequate,it might help.
If you are able to set up a login account at the cisco web site you can look at the release notes for the different SW versions & see the fixes & caveats for each.
Use portfast with caution, Portfast on all blades can be dangerous if you have redundant links. Only use portfast on ports to end stations.
Good Luck,
ACAC