The Overclocker Café have posted up a short guide on GPU heatsink/fan removal in response to a number of emails asking how this can be done. Here is a snippet:
"We were modding our Chaintech GeForce4 Ti-4200 with some RAM sinks and decided to attach a Tt Crystal ORB chipset cooler to the GPU using Arctic Silver Thermal Epoxy. Once this dried, we had a victim for our surgery. As with any modding, you need to exercise the utmost caution when working on components otherwise you will be reaching for the Kleenex."