problem is likely to be a task running over the network (or at least failing). when the machine hangs, does ctrl+alt+del show a task running? things that pop to mind are SMS (yuk). Also running a large document open over a LAN regularly hangs fragile Win98 machines. (I always copy big docs down, work on them, then copy back up at the end).
I concur with previous post.. unless NETBeui is there for a reason (unlikely), remove it. Not only does it increase overhead, but if your network is connected to the internet, it also presents a gaping security flaw.
MP