Any motherboard made in the last 2 or 3 years will work fine (probably older too). If it can even SEE a 60GB hard drive it'll be fine.
I'm not sure how well moving WinME to the second drive would work. The master boot record is currently looking for the OS partition on the first drive. If you move it off that drive, you won't be able to boot.
I'm not sure what you mean about it having to go through the slower drive. You should always make your faster drive the main hard drive (primary controller, master) and install your primary OS on it.
Are you sure the 20GB drive is actually slower? A lot of larger drives are actually slower than smaller drives (increased seek time and/or lower rotation speed).
If you're going to be installing WinME fresh as well as XP, then just install WinMe on the second drive (you'll want to create all your partitions first, so that WinMe doesn't think it's on the C drive and then you change the drive letters around when you install XP). Then install XP in the first partition on the first hard drive. XP will install it's own boot loader, so you select which OS to use every time you boot. If you do it the other way around, the boot loader will still be installed to whatever the first drive is.
Here's my setup:
drive0: C drive with Win98SE, E drive with WinXP
drive1: D drive random stuff, F drive random stuff
For some reason I found this easier to do than installing XP on the second drive (slightly slower, but probably would be faster than where it is now, since it could have gone to the beginning of the drive instead of the middle). I think I just had partitions in place already on the second drive and didn't want to move them around.