I've a much simpler system, and I'm getting 16 tracks (16Bit 44.1Khz) no sweat.
That's using Logic Audio 5.5, a Athlon 1.7GHz, and standard 7200 RPM drives.
Your PC should be able to handle this without such hicups...
One thing to try is adding a IDE controller PCI card and attacthing only the drives that you use for audio.
Keep your DVD / CD ROM drives on the IDE slots on the motherboard, and your System harddrive on the IDE primary of the motherboard.

BTW - What program are you using?