Pretty much any large brand motherboard these days is “stable”. I’ve used Soltek, Biostar, ASUS, MSI, and Gigabyte. Never had a problem. The people who complain about “instability” are usually the ones trying to overclock their CPUs.
Now that we have an idea for what you want to do. I recommend the following:
-KT400 AMD Motherboard (USB 2.0, Firewire on board, ATA133)
-Any recent CPU - I run a Duron 1.3 and my CPU load never gets above 30%
-A large heatsink-fan unit - I personally prefer quiet ones because some can sound like a hair dryer
-512MB+ PC2100 or 2700 RAM (Choose a name brand like Transcend)
-ATA 133 hard disk (Seagate and Western Digital are know to be more quiet)
-350W power supply to power the sucker (Seventeam, Antec or other big brand)
I strongly encourage you put this together with a friend who has put one together recently. With CPUs these days, screw up putting on the fan and watch it go up in smoke.
Another possible reason why your computer was running slow was that it was loaded down with stuff like RealPlayer agent, WinAmp agent, Bonzi buddy, hotbar, and all other sorts of evil programs like that. You’ll simply have to watch out. I’ve seen very high-spec systems completely loaded down by those things.