Hmm. Not sure about changing your drive letter. Mine's not standard (F) but I can't recall having any real problems with it.
You probably know this, but to scan CDs, you need to select "Tools->Download from CDDB" and from the resulting window, enable 'Auto Scan' from the Options menu and change the 'Auto Scan Interval' to the minimum (1 second). Pop in a CD, it gets scanned and out it pops again. And repeat for however many CDs you've got to hand and once you're done, select 'Download' from the 'File' menu to retrieve the relevant info for all the CDs you've scanned...alter any info you're not happy with and then 'transfer' to your library proper.
I find it works quite well.

I've scanned 1200 CDs anyway, with no problems.