Windows ME = shit.
A lot of music people seem to use Windows98SE or Windows XP. Computer geeks favor either Windows 2000 or XP.
If you're having MIDI problems, my guess would be that you're using a serial > MIDI adapter and you have a cheapo motherboard. For that system, you could try a dedicated MIDI interface, but since you're getting a new computer altogether, research your mobo's and get a feel for which companies release quality and which ones release shit. Compaq/Dell/Gateway are more likely to give you shit mobo's, even though I must say that even my craptastic Compaq that I used for 2 years could handle MIDI without a hitch.
Personally, I use Windows 98se with Logic Gold 4.8. Emagic strongly suggested that people use win98 with version 4, and finally released version 5 earlier this year which was compatible with XP. Then in July Apple bought emagic and dropped PC support.