If the Fast Track Pro correctly works with your Windows PC, you should be able to play plugins with a buffersize of 128 samples. I had the FTP running on my Armada notebook (600mhz, 256mb ram, xp) really smoothly with latency of 128 samples. However, if I connected the same FTP to another faster Compaq notebook, I had glitches and crackles constantly. This was possibly caused by IRQ sharing conflicts
Also, keep in mind, if you use the SPDIF connection, you can't monitor your audio with zero latency settings.. You need to run the incoming audio signal through the software (Ableton) to be able to hear it. The zero latency monitoring option is only available for the analog inputs, which was the reason I sold it.