I've had a cuecat around for a few months now that I got from my grandmother. I finally decided to open it up today when I wanted to add a bunch of books. Unfortunately, the cuecat driver software doesn't work on windows 7 (or work very well on windows xp for that matter). This isn't a huge deal, however, as the original cuecat driver software phoned home (I wouldn't use it anyways).
I have a ps/2 cuecat, and it doesn't work at all with my dual ps/2 kb/mouse to single usb adapter. I finally got it working by plugging it directly into the back of the computer and plugging the keyboard into it (it has a plug for this).
There's still a couple problems with this, though:
1. the cuecat doesn't send the barcode data straight--it has to be decoded.
2. Bookmooch does not accept UPCs, and the barcodes on books aren't usually the ISBN, though I found a couple that had the whole ISBN inside the upc.
To solve #1, I found several websites and scripts that will decoded the text. Just put the cursor inside the text box, and scan your upc; the when you click the button, it will decode the upc for you, and tell you if its valid (using the check digit).
To solve #2, I found this great site: http://www.kayaker.net/cuecat/upc5.php. It works just like the above solution, only its specialized for books--it gives you both an isbn-10 and an isbn-13 for any valid book upc you scan in.

I still find it somewhat simpler to use the website I posted--it takes the encoded cuecat output and gives me an ISBN. I highly doubt linux will give you the ISBN number; I find it more likely that it would give me the UPC+5, and then I would need to find a different script to convert those.