Oh, I imagine that motherboard is ATX as almost all are now. That sounds like a fine solution to me. But, it really depends on how fast is the CPU he currently has to determine if it's a smart solution. I mean, I wouldn't do that if he has a 500MHz PIII. I'd go ahead and get a 1.2GHz motherboard/CPU/fan combo for about $150. There are some good combos out there for this price now.
I just wouldn't advise a new motherboard for someone with a processor of less than 800MHz today. Seems like a waste of money for something you won't be happy with in a year. It does depend on what you want to do with the PC. If you are not a power user, that would mean a slower PC would do fine for you longer. But, if you want to play games all bets are off. Nothing pushes PC sales and upgrades like PC game playing.
I afree completely. But money gets tight. You can upgrade the board, then the vid card and finally the CPU. over time its much less painful. :) And the ASUS C2SL2 supports the fastest PIIIs. :)