I have a debian box with two network cards and a Motorola SB4200 Cable modem (using USB).

eth0 - Primary network card, connected to hub - AMD Internal Ethernet Card
eth1 - Inactive - Realtek Ethernet Controller
eth2 - USB Cable Modem - Motorola SB4200 cable modem.

All devices are correctly configured and there are no current IPtables rules.
The other two computers that are being used are two WinXP machines, all in the 192.168.10.x Class C address range.
The Debian machine can ping any of its own interfaces, but trying to ping any of the other machines results in a 'destination host unreachable' error. The hub is working fine, and the other two machines can communicate fine with each other. Different cables have been tested, and the Debian machine worked fine under WinXP.
Pinging 192.168.10.255 from the Debian box results in only responses from itself.

Any help would be greatly appricated.

Are all your boxes are using class C address?

Yep, they're all class C.
The problem was the card I thought was eth0 was eth1 and the other way around. -_-"
Also eth1 (acutally active) doesn't seem to work under linux. Under eth0 there are no poblems.
Also, the cable modem wasn't under DHCP due to binding problems or some such, I'm not sure that's the right way to say that. Either way, it's all been resolved. Thanks.