WinME is the "step up" from Win98SE ... Unfortunately it is increasingly unstable, significantly slower and more resource demanding, etc.
Most people don't realize how crappy WinME is, because it comes with their computer and they think it's good just 'because'. But it isn't, it does indeed suck. Microsoft really botched this one up. Now there's even less DOS.. What did that give Win9x? Nothing! DOS just allowed people to do more... Removing bits of DOS from Win9x does not make it more stable... WinME is seriously a botched up Win98!
It's my opinion that Windows 98SE and Win2K are the two best releases of Windows to date. While Windows 98 does not have the stability of Windows 2000, it's still stable enough for the average user and handles games nicely, while also having a huge compatibility base. It also is not too demanding (I've seen sub-100MHz run Win98 nicely, you just have to set it up properly).
If you're going to support Microsoft, use Windows 98 or Windows 2000.

Otherwise stick with BeOS and/or Linux (LIE-NUX dammit.. 'linnux' sounds dumb and makes no sense). Some stores are selling their systems with Linux now, it's nice to see that happening.