I too have thought about doing this...
From what research that I have done:
First of all, you'll need to get a 9500 non-pro card using a red PCB where the memory chips are laid out in an "L" Shape (2 chips above and 2 chips beside the GPU fan). If you have a card that has all 4 chips in one row, it will not work (fully, at least).
The reason it works is because some of the earlier-produced cards were essentially the same board as the 9700 card, they just scaled it down to "9500 speeds". If you look on the actual hardware, there are actually 8 pipelines on these versions of the 9500 non-pro cards. 4 of them are disabled (and untested).
The various "software mods" for this essentially enable the extra 4 pipelines on the card. Sometimes, it will be a great success, while other times it will not. Notice that I said the extra 4 pipelines were untested - this means that ATI/Sapphire/etc only tested the 4 enabled pipelines for these 9500np cards, and shipped them out. They did not test the card for all 8 pipelines working. It is quite possible that you could get a card where not all 8 pipelines work completely correct because the extra 4 were not factory tested!
Some people experience various "artifacting" and "checkerboarding" whenever they perform the mod, and I believe that it's for this various reason. Many polls have concluded that there is only about a 60-70% success rate for doing this mod.
Also, with this mod you are taking a 9500 non-pro to a 9700 non-pro. You only achive the "Pro" status by overclocking both the core and memory to faster speeds, therefore sort of "simulating" the performance of a 9700 Pro card.
For more information and possible download, check here:
http://www.maxdownloads.com/~ian/wizzard/
Again, this is just information that I have gathered through my limited research time on the subject.
