I agree, dm7941, out of all the board manufacturers on the market, Asus seem to deliver consistantly good products.
RGC, if you've had 100% failure rate with Asus boards, I would think you very unlucky!
Abit and Tyan are my (personal) 2nd and 3rd choices for motherboards, respectively.
With a good PnP board and O/S, IRQs should not be an issue: the Promise card is good, as is the Abit Hotrod. You do not have to use the RAID features of the card, and it will certainly give you extra IDE channels.
Also, if you're installing these machines in schools, I would suggest that you do not overclock the processors. This practice is fine for home PCs, but generally unnecessary for this kind of environment - and could lead to the problems you are experiencing. Although I understand that Asus boards are particularly good for overclocking!
I hope this information is useful