Just because it is a different device will mean that you will not be able to access it the same way you would access a serial communication. I mean, it's possible to write wrappers and everything to create that functionality, but you will need to access it differently, just because it is a USB device and not a serial device.
What version of Debian? Did you check the /media folder?
Following is the system details
Linux debianTSP 2.6.18-4-686 #1
Also i checked the media folder so it shows me the usbdisk dir created over there.
I want to access any of the following using C program
debianTSP:/media/usbdisk# ls -lart /dev/u*
crw-rw-rw- 1 root root 442, 0 2007-08-31 12:24 /dev/usbdev1.1_ep00
crw-rw---- 1 root root 442, 0 2007-08-31 12:24 /dev/usbdev1.1_ep81
crw-rw---- 1 root root 442, 1 2007-08-31 12:24 /dev/usbdev1.2_ep00
crw-rw---- 1 root root 442, 1 2007-08-31 12:24 /dev/usbdev1.2_ep81