ducati996 yes it would cancel warranty,but I am still going to do it myself with the 9800gtx.all stock gpu,cpu heatsinks and fans are junk.go figure they sell you a pricey cpu or video card and they slap a $3.00 heatsink and fan on it.
I'm not worried about warranty I want the gpu or cpu to run cool and stable.also I have been building my on pc for the last 16 years never had a warranty issue.
you could also replace it and keep the old one encase you needed to put it back on and send it in for warranty.hope this helps you out.lol