I did get timidity midi playback on an Abit NF7-S (nforce2). The key for me was to use the virtural midi player in the kernel.
I added the following to my /etc/modprobe.conf file and it works.
# Configure card 1 (second card) as a virtual MIDI card
alias sound-slot-1 snd-card-1
alias snd-card-1 snd-virmidi
I am using a kernel.org 2.6.7 kernel on a Fedora Core 2 base system. Give it a go and see if it helps....