To upgrade BIOS under windows XP is not that much of a task, but then, it is not that simple too. First, you need to boot to DOS, if you want them to run as most BIOS programs need you to boot to Disk Operating System. It is actually a safety precaution. You may have to drive the motherboard back to the manufacturer to have the BIOS reinstalled if Microsoft Windows XP were to stop working for the duration of a BIOS upgrade. Upgrading it is one of the activities like don’t fix it unless broken.
Unless you have a specific problem that only a BIOS flash will fix, search for an alternative. Only a detailed / explicit elucidation of the BIOS flash and the problem it is to fix will support the need for the upgrade. Only the MOBO manufacturer will know if the Flash will help. If you’re only upgrading because it may help, then it most likely won’t. And there is a high probability you will destroy your BIOS in the process. If after each effort fails, you still see the necessity to upgrade, find a reliable PC technician and have them carry out the Flash. So, one should be careful while upgrading BIOS. Upgrading it with out any pertinent knowledge is not advisable.