Adam:
Does dmesg say anything about the printer being plugged in? If not then can you see the printer appear on the usb bus if you boot the machine from a linux live cd with a different kernel version or something? Also, have you checked and swapped cables for known good ones and used the same usb ports for both tests? I'll admit i'm a bit stumped too.
dmesg: no. It reports usb 1-2: usbfs: USBDEVFS_CONTROL failed cmd hpiod rqt 161 rq 1 len 1 ret -110 every so often so it knows something is there though. I also haven't checked the cable - I'll have to wait till I'm physically there again now. I tried both usb ports. I'll also try the reboot with live cd when there if still not solved, and try the printer back on the old computer it was on to see what messages I can get.
Keith:
Have you got USB support ? Its an old one, but try lsmod and see if anything USB is in there.
Yes: other usb devices work fine, using OHCI module.
Thanks for the comments,
Jenny