You can't mess your device up, permanently, with ROMs. The worst you can do is get in a boot loop, which can be fixed by pulling the battery, force rebooting, or waiting for the battery to die. Radios are the thing you have to be careful with (which may or may not apply to you). Just throwing that out there so you don't worry.
Well download ROM Manager from the market and press flash recovery when you open it, then select you device model, DO NOT LET THE SCREEN TURN OFF AND MAKE SURE THAT YOU ACCEPT SUPERUSER PERMISSIONS (if you don't have superuser, download that first.
Choose from some of these roms below - http://forum.xda-developers.com/showthread.php?t=1674827 -AndroWook Prime http://forum.xda-developers.com/showthread.php?t=1582907 - CM9 (Stock Android 4.0) http://forum.xda-developers.com/showthread.php?t=1660773 - Gummy ROM (One of the most customizable CM9 ROM) http://forum.xda-developers.com/showthread.php?t=1576937 - TOUCH RECOVERY (will explain after) IS YOUR TABLET UNLOCK (like in a bootloader unlocked)?
Well, today I unlock my Atrix bootloader, if you haven't had any problems with the tablet do it. First, see if it causes any OS changes, like on my Atrix is shown UNLOCKED when I booted up, but you can hide that, so there is no other way of knowing that the bootloader is unlocked. So if you can find a way to hide the bootloader is unlocked, go for it.