Unable to see arduino using Debian Squeeze

I'm using Debian Squeeze and an Arduino Uno. I have installed the IDE version 0022 and I connect the Uno to my PC using my printer cable (so I am confident that the USB connection works), but the IDE can often only see /dev/ttys0. Sometimes it can see /dev/ACM0, but not always. However, even when I can select that port, I cannot upload a sketch - I always get an error message:

avrdude: stk500_recv(): programmer is not responding

I can see that the necessary USB port exists:

ls /dev/tty*
... /dev/ttyACM0 /dev/tty13....

but the IDE usually doesn't seem to be able to see it. Sometimes though I can select the ACM0 port in the iDE, but that still doesn't solve the uploading problem.

Does any one have any guidance on what I must do to fix this?

TIA

what is the output of dmesg when you plug your uno in?

Here it is:

[ 302.608028] usb 3-1: new full speed USB device using uhci_hcd and address 2
[ 302.806164] usb 3-1: New USB device found, idVendor=2341, idProduct=0001
[ 302.806171] usb 3-1: New USB device strings: Mfr=1, Product=2, SerialNumber=220
[ 302.806175] usb 3-1: Product: Arduino Uno
[ 302.806178] usb 3-1: Manufacturer: Arduino (www.arduino.cc)
[ 302.806181] usb 3-1: SerialNumber: 64932343738351C09091
[ 302.807647] usb 3-1: configuration #1 chosen from 1 choice
[ 302.887670] cdc_acm 3-1:1.0: ttyACM0: USB ACM device
[ 302.890641] usbcore: registered new interface driver cdc_acm
[ 302.891677] cdc_acm: v0.26:USB Abstract Control Model driver for USB modems and ISDN adapters

At this point I can 'see' ttyACM0 in the IDE, but as soon as I attempt to upload a sketch it disappears from the IDE, leaving ttyS0 as the only serial port, which doesn't work.

TIA