Thanks! I had to create /lib/modules/2.6.19/ but then it worked. However, now when I run modprobe I get the error:

FATAL: Module usbserial not found.

I guess I have to face the fact that this kernel doesn't have USB-Serial support built in. I've been trying to compile a module as I have some source code for a driver for the specific device, but cross-platform kernel module compilation is a bit beyond me...