Willametta P4 was a fine processor, but I only used it in the 1.8Ghz to 2.0Ghz range. When I tried to use a Celeron 1.7Ghz, same CPU size, it dropped frames on MPEG capture. In fact, that system dropped frames on AVI capture, because the VIA drivers were crap.
AVI capturing is mostly an exercise in I/O. And I/O is not as simple as using a fast hard drive -- the computer has to be good at using the fast hard drive! Most motherboards of that era are complete crap, VIA based, and had rotten VIA drivers. It's been too many years to recall if that Asus was good or a problem. All I can say for certain is that Asus was using Intel and not VIA chips during the earlier years of the past decade (2000-2002), and should be okay. You'd really just need to put it together and try some captures. I may have used that exact mobo at one point.
The SSE2/SSE3 doesn't really matter for AVI capturing. That was most helpful for using the live MPEG-2 capturing function of the ATI AIW cards. Though it was partial hardware (hybrid) encoding, it still needed some CPU cycles. I forget which portion of encoding was kept on-chip, and which was fed to the CPU. (The prevailing theory of the day was that you'd be able to get better encoding as CPUs increased. Big names like Matrox and Canopus were big supporters of this. The idea fizzled around 2005, as NLE card manufacturers dropped it.)
I'd stick to Huffyuv
-- not newer AVI compression codecs, which tend to be greedier on CPU.