Overclockers.com have developed a PCI latency timer that can modify most, if not all, PCI latency timers on motherboards with VIA chipsets!

Here's what they're saying:

This utility will allow the modification or display of the PCI latency timer of a PCI device if its PCI latency timer is located at offset D. I've used it to modify the PCI latency timer of modems, VIA EIDE controllers and sound cards. Curiously I'm surprised a modem would be capable of bus-mastering at all -- considering it has got to be the slowest device you can find on the PCI bus. Download PCITIMER v2.0