at the moment AFAIK there is no special howto for building rt-n-alpha branch. However, you can use as a base the following instruction: http://code.google.com/p/wl500g/wiki...CustomFirmware However, it is only a way..., but not a strict guideline.

IMHO, you have to first learn how to compile the firmware using a dedicated toolchan. The next step is to enable some extra options in the kernel config and recompile it again to produce custom module. I don't see a way to avoid these steps.