Changes 1.8:
Simplified tha patching mechanism to solve some problems with nags and server R2. Instructions below still apply

Changes 1.7

Completely new patching mechanism, upgrade reccomended! Details below.

The new patching mechanism disables the software licensing entirely from the OS, and there are a few things to take note of:

MAKE SURE TO INSTALL KB974431 FIRST BEFORE PATCHING OR SLIPSTREAM INTO YOUR ISO IF YOU'RE USING THE /S SWITCH!

If you come across an update (SP1 for example :P) that you cannot install, you can just restore WAT and install the update, then patch again ;)

IF YOUR SYSTEM HAS ALREADY EXCEEDED THE TRIAL PERIOD:

Set BIOS clock back so you are back in trial period, then patch, then set the clock right again ;)