OS X V10.5 Leopard :: Get CanoScan To Work (extra)?

I have an old CanoScan LIDE N670U scanner which worked fine on a G5 iMac in Tiger (through Photoshop 7). I now have Leopard on a G4 Powerbook and cannot get the scanner to work through Photoshop CS. This is what I've tried : Downloaded the CanoScan Toolbox for Mac OS X - this launches VISE which begins the installation then tells me it has failed because "You do not have enough access privileges". I'm doing this in my admin account! Same thing happened after restarting Mac and redownloading the software.Downloaded the CanoScan driver for Mac OS X (the latest version - 7.0.1) which extracted to a folder of plugins etc, and an installer. Running the installer produced two error messages (regarding a .shlb file and a Button Manager) but completed and has installed the driver into Photoshop CS > Plugins > Import / Export.When I run Photoshop CS, the CanoScan appears to be there in the Import menu, but when I select it I get an error message saying the necessary file is missing or damaged, please reinstall driver, driver window will be closed. I've tried all this a few times with the same result each time. 

I urgently need to get some scanning done this weekend, please help! 

Extra info - I found a backup of the CanoScan Toolbox 4.1 which I copied over into my Applications folder. The original installer log says there should also be a file Macintosh HD:Library:CFMSupport:pafcv2_carb.lib which unfortunately I cannot replicate without doing the installation (see above). However I'm still getting the same error in Photoshop. And launching the Toolbox doesn't help either - the interface is there but it won't select any program to link to. The driver in the Toolbox appears to be exactly the same as the driver I downloaded separately and installed into Photoshop CS.  

Info:
PowerBook, Mac OS X (10.5.8), G4, 1.67GHz, 1GB RAM, 250GB HD