You need to find out your Current GPU Core . If its an R360, you can do it.
Use ATITool to check the REAL GPU core version. dump the BIOS to your Hard
drive, examine it with Notepad to see which to find out which memory chips
your 9800Pro uses,(Samsung, Hynix etc)... then Find the Correct XTBios, I
had to use a "ClubXT bios" or something.
Flash it, with a Flasher (From DOS, not Windows,,, windows didn;t work for
me), Unistall the ATI catalyst Drivers, Reinstall them etc.
Cross your fingers...
It worked for me. My Sapphire 9800Pro(128Mb), is now a 9800XT (without the
Temperature Sensor though, and obviously with the same 128MB). The Clock
speeds are increased now By default with the new XT bios..
anyway.....Here is the more info on how to do it
http://www.rojakpot.com/default.aspx?location=3&var1=92&var2=0
Maybe another website will have more exact info for you,