HP TC4200 Tablet problem: Repeated hangs

I have a new HP TC4200 Tablet PC using Windows XP Professional 2002 for Tablet PC (SP 2) with an Intel Pentium M processor, 512 MB + 533 MHz DDR2 SDRAM, 60 GB HD, and have run into a problem (among many others): After the computer has been running for a while, I end up with erratic behavior that could best be described as repeated "hangs" or "hesitations." That is, if I am moving my cursor, or scolling in a document, or doing pretty much anything else, the computer hangs momentarily then executes part of the action, then hangs, then executes, etc., etc. For example, let's say I want to scroll down a document; it might scroll a few lines, then hesitate for a few seconds, then scroll a couple more, hesitate, scroll quite a bit, hesitate, etc. Same with cursor movement. One curious behavior is that it seems to worsen when the internal fan turns on or increases speed. I downloaded Process Explorer and run it when I am having a problem. It indicates that, when the problem occurs, the RAM is maxed out (although it shouldn't be, given what is running). I have contacted HP and have done the following: Updated the flash BIOS, did HDD test (OK), removed the extended memory module and reseated, did a system restore, reloaded all drivers, updated all drivers and programs, opened in safe mode, and unloaded startup programs. Nothing worked. HP wants me to send it back for repair, but this seems like a solvable problem. Can anyone help?
Thanks,
Richard Shelton