Ok i have the same grafix card it does get hot! as far as i know the fan fix wont void warrenty or anything of the sort as it is just changing a few paremeters to allow the fan to constantly spin at a higher RPM.
there are alot of threads all ova the place that deal with this but here's how u do it manualy.
Make sure you have "show hidden folders enabled.
first go into catalyst and make a new profile. Up at the top where it says profile, then the little arrow over and name it whatever you want. After creating it leave catalyst.
Then do this.
if running vista
C:\users\yourusername\Appdata\Local\ATI\ACE\Profiles\profileyoujustmade
right click and edit that file.
Got the bottom and you will see this text
<Feature name="FanSpeedProtocol_1">
<Property name="FanSpeedProtocolProperty" value="Percent" />
</Feature>
<Feature name="FanSpeedAlgorithm_1">
<Property name="FanSpeedAlgorithm" value="Automatic" />
</Feature>
<Feature name="FanSpeedRPMTarget_1">
<Property name="Want" value="1376" />
</Feature>
<Feature name="FanSpeedPercentTarget_1">
<Property name="Want" value="27" />
Change Automatic to manual and then change the 27 to whatever you want. i perfer 65
on my machine where it said
<Feature name="FanSpeedAlgorithm_1"> it was a 0 instead of a 1 make sure that it reads 1 and not 0 or it will not work!
here is what it looks like when done
<Feature name="FanSpeedProtocol_1">
<Property name="FanSpeedProtocolProperty" value="Percent" />
</Feature>
<Feature name="FanSpeedAlgorithm_1">
<Property name="FanSpeedAlgorithm" value="Manual" />
</Feature>
<Feature name="FanSpeedRPMTarget_1">
<Property name="Want" value="1376" />
</Feature>
<Feature name="FanSpeedPercentTarget_1">
<Property name="Want" value="65" />
On XP the only difference is how you find the profile.
should be
c:\document and setting\yourname\application data\ATI\ACE\profile
after you do this, re-open catalyst and run that profile, some say you have to do it everytime. For me, i have only had to do it once and it does it on boot up
Another note u may have to reload the profile everytime u start windows im not sure mine does it automaticaly!
another way u can do it is using a application such as 'ATI Tray Tools'
http://www.ngohq.com/news/14562-permanent-fanfix-radeon-hd-4800-series.html
there is a link to the latest 1 that should have support for the 4800 series!
i havnt tried it as of yet i will when i get home this afternoon!
hope this helps!
good luck