I put together this small computer which will be used to control the lathe. The components for this kind of box are quite inexpensive:
D945GCLF2 motherboard including 1.6 GHz Atom330 CPU, 76 eur
Codegen MX31 case including 420W PSU, 46 eur
2Gb DDR2 memory stick, 46eur
Samsung 320Gb HDD, 44eur
Labtec keyaboard + mouse, 17eur

Total:  229 eur (no display) parts from jimms-pc and verkkokauppa.com

The motherboard has one PCI-slot for a Mesa 5I20 FPGA-card which provides 72 digital I/O pins for real-time control.

Here is the D945GCLF2 motherboard. The CPU doesn't need a fan, but there is a small fan for the PCI-controller(?).

Realtime performaceshould be OK, I was getting about 10 us of jitter for a 1 ms thread.