Interesting; we're in the same boat! I have the KT7Raid. The 133FSB Athlon C will run on this board, just not at the 133FSB, it'll run at 100. As for just updating the bios, nope. The KT7A and other KT133A boards use a different via chipset, the KT133a, as opposed to just the KT133. The "A" denotes 133 FSB speed.
I was thinking about upgrading (don't really need to...but you know the story!) to an Athlon C about 6 weeks ago. But then DDR started taking off, and DDR prices dropping. Then, the Athlon 4 got announced....blah, blah, blah. I'm going to stick w/my rig for quite awhile. I just recently got another 256mb of ram for a total of 512. Humming along quite happily, and quickly too! If I do anything, it'll be get a GF3, sometime in late Fall/early Winter. By then the Raedon 2 (or whatever that ATI card is gonna be called) and the GF3 Ultra/Super/Mega/Whateva will be out, dropping the price to something within the reach of mere mortals.
What speed CPU do you have now and what speed are you running at? If at least 900, your golden. How about memory?