I just got a 2500 and an SLK-900 yesterday. To install you need to basically take you mobo out of the caseas you need to mount a plate behind the mobo that the heat sink will screw into (actually I didn't take it out all the, just enough to reach around the back). That would have been annoying if hadn't been planning on rewiring my case anyway as it was getting very cluttered.
I however did have a big problem getting the heat sink it self to fit. I've got an A7N8X dlx (not sure what version, bought about 6 months ago or so) and the capacitors near the socket and the northbridge heat sink were in the way, if just barely. At first I tried using me dremel to grind the fins of the SLK-900 down a bit but that just wasn't working. Basically I just bent in the fins a little on one side and pretty much just forced it. Luckily I didn;t break anything as my comp powered on fine. My temps did drop about 5ºC from my 2100/SK-7 setup. I think I can probably reseat the heat sink and get a little lower.
Btw I use Thermaltakes Smart Case Fan II, they rock, even if the orange is a bit gaudy. At max speed they can be pretty loud but they move a LOT of air, and you have some choices on controlling there speed. I actually have 3 in my case right now.