Upon procuring a new video card I am now installing my radeon 9800pro in a non-watercooled system, thus requiring the reinstallation of the stock HSF. Does the stock cooler require a thermal adhsive or a thermal paste and is reinstallation even possible? (I have the spring loaded screw things that originally held it down)

just put some Arctic Silver or Ceramique on the GPU and then re-install with the spring-screws. Plenty of people do this (re-install stock cooler) in order to lap it, use AS or remove the shim

Yes it is possible to re-aply it and you are probably going to have to use those spring loaded screws, unless you get an after market heat sink. Thermal paste is the way to go since that is what was on it in the begining.

...And Make sure to clean off the old HSF with acetone or MEK, first...then the GPU and don't be tight with the Ceramique...there is quite a gap if the shim is still on the card.

Seat it square on the GPU then push the pins till they click. If the old pins have been damaged at all, don't risk it...Go out a buy some Nylon #5-32 thread bolts, washers and nuts. Really cheap insurance to keep the stock fan on...

Thanks for the help. With the pins clicked in place though, the heatsink still seems to me to be rather loose. How much pressure is needed as with the pins all the way in, as the heat sink can still be moved a few mm left or right?
Also, when removing the HS, I seem to remember a little pin which had to be pushed upwards before both sides of the fastener were pressed together and the fastener pushed upwards and out of the card. This little pin in between the two halves is now absent. I may be thinking of the CPU HS though.

EDIT: I checked my old "removing 9800 heatsink" thread and it seems it did have a pin in it. Which I have since lost. Do they sell replacement spring loaded screws?