In the FAQ section for the KG7, the site even explains that the BIOS update is only to change the way the name of the CPU is shown. It will support your XP even without the 5E update, you would just have to set the CPU clock speeds yourself, and they have a table to show you what settings go with which processor model.
<A HREF="http://www.abit-usa.com/eng/faq/kg7-raid.htm" target="_new">http://www.abit-usa.com/eng/faq/kg7-raid.htm</A>
I only mention this because some systems have had a difficulty with CDROM recognition under windows 98 and the 5E BIOS.
"Paul's unofficial KG7-Raid FAQ" mentions this Look under BIOS section, "what are the differences in KG7 BIOS versions?"
<A HREF="http://www.viahardware.com/faq/kg7kr7/bios.htm#What is the latest KG7-RAID beta BIOS version?" target="_new">http://www.viahardware.com/faq/kg7kr7/bios.htm#What is the latest KG7-RAID beta BIOS version?</A>