If you have all the correct drivers for the hardware (and have them ready to install in advance) ... Windows 2000 Pro is the best combination of stability and speed.
I wouldn't install WinME, not for any amount of money. Too many Plug-and Play issues and 16bit virtual device driver issues. I shudder to think of running a Win9x OS without decent control at the command line.
Win98SE is more robust than WinME ... but requires too much maintenance, in my option. But any version of Win9x tends to be "fragile", and it doesn't take much to screw up the system. That's the price for backwards-compatibility with older programs.
Of course, you could always go with Linux, which puts all the Windows operating systems to shame in terms of stability. But that's a completely different ball of wax.
My two cents.
Toejam31
<font color=purple>If there was a reason for everything, having faith would be redundant.</font color=purple>