I just installed one of these over the stock AMD HSF, my system specs are:
Athlon XP 1900+
2x 256MB Kingsmax PC2700
Soltek SL-DRV5 board
Asus Geforce4MX 440 64MB
SB Audigy
PCI 56kmodem
2x WD HDD's
DVD + CD-RW

When i installed the the new HSF everything seemed ok, i linked it to take power from the PSU (Antec True330) and all seemed well until i started testing 3dmark and some games. It would crash about 2 seconds into anything 3D accelerated. So then i tried tweaking the Bios and lowering some speed settings, AGP, Voltage in case it was the out of power, but no effect. Then it started crashing in winXP and Win 98, so i figured it must be a power issue, so i gave up for the night. This morning though, it seems to be working perfectly. So could this be a heat issue? i'm still half afraid it might happen again.

get motherboard monitor and run a prime number benchmarching program like prime95 or similar. watch the temps increase and see how hot it gets and how fast it gets there. it should take about 5-10 minutes to get up to about ~60-65 and shouldn't get any higher if you have installed the heatsink properly.
my friend has one of them, that has the speed switch right? when doing any thing intensive, make sure it is on fast (sure it's loud but thats the price you pay
you also need adequate case cooling, if you don't, run the tests with the case side off so that you can visually monitor the fan speed to see if it isn't a power problem (or in the switch maybe) that's causing it.
also sometimes it can be tricky simply installing a HSF, if you are satisfied with the temps and think you can install it better, following the instructions at http://www.arcticsilver.com are quite good.

basically, you take off the HSF, then clean the old goo off the HSF bottom and the top of the CPU with 99% pure isopropyl alcohol. having the right alcohol is IMPORTANT. i have gotten away with using 85% pure before so that would be okay, but try for at least 95% purity (goto a good chemist).

squirt a bit of as3 or any other very good thermal goo on the HSF bottom and polish it in using a paper towel. (it should look smooth, shiny)
then place a very thin layer of goo on the top of the CPU so it covers all of it. then place the HSF straight down on the CPU, without sliding it to any side. that's the hard part. put the clips in place without sliding it (or as little as possible).

also, why can't the fan run from the mobo's fan connector?

also, set everything in your BIOS back to your normal operations, minus any overclocking, decreasing voltages will decrease stability

if u have 7+ which mounts with just one clip, those problems can occure, cause of not enough force to firmly press the processor.

thanks for the replies, i've been using the computer all day and it seems alright now. Its idling at about 33-35C, and seems to max out at 51C which is way better than the stock HSF temps.
I might try that Prime95 test on it still, but it all seems fine now.
It runs off the power supply because that's the connection it uses in combo with the fan speed selector.