Is it just one machine you have these latency problems with, or is it more than one?

By the way: If you need a permanent machine for collecting the data, I think this may be an interesting solution:
http://www.tranquilpc-shop.co.uk/acatalog/...GCLF2.html

It is cheap and reasonably low-power (they "forget" to tell that the 4W processor is mated with a 22W chipset...) so you could use it as a dedicated machine for this task. And with Linux (or maybe some older OS you have laying around) you don't need to spend money on any OS. Having a dual-core, hyperthreaded, processor means it can run four applications at a time which would be advantageous for minimizing latencies.

There are also complete machines available if you don't want to spend the time figuring out the best case to use.

If your sensor system can send using USB or Ethernet, then I don't think you would need any separate buffering if you are a bit careful with your installation. And the PCI slot would allow a synchronous serial board if the sensor system can't support USB or Ethernet. I would expect a synchronous communication board capable of 10Mbit transfers to have enough buffer capacity to make sure it can run continuously without dropping data - after all, the expected target OS for such a communications board would be Windows or Linux.