First you need to do some recommended reading to understand how this awkward system of flashing from heimdall and the various recoveries.
This explains what can happen to your tab should you mess up.
This explains how to revive your tab from that mess if it is possible. Also shows you how heimdall works.
Finally, this shows you how ClockworkMod Recovery works. To get to CWM Recovery on the galaxy tab hold volume up and the power button.
This should give you an idea of what can go wrong and how to fix it. Read carefully because you can disable your device to a point where you can't fix it and will have to send it to somebody who can.
Now there are two ways you can proceed from where you are at:
Flash a rom that doesn't have assert problems in the version of ClockworkMod Recovery that you have installed.
Directly flash a recovery and kernel from heimdall.
The easier and safer route is to just flash one of the roms that can be flashed from your CWM Recovery. This one will give you a working MIUI rom and CWM Recovery 5. Just follow the instructions from the CWM Recovery tutorial I posted and the instructions from this link.
The second route will give you experience on heimdall. Recoveries can be flashed using a recovery.bin and a ZImage file in heimdall. This will let you put CWM Recovery 5 on your tab no matter what rom is installed on it. Unfortunately the zImage kernel is not compatible with the stock rom so once you install this you will only be able to start the device into CWM Recovery.
- CWM Recovery 5 recovery.bin & zImage
To install fire up heimdall after reviewing the directions from the return to stock/heimdall tutorial and put recovery.bin in the recovery slot and zImage in the kernel slot.