Still trying to find out more on your scanner, but it looks like you've got 600x1200 optical and 9600x9600 interpolated.
Does the "light lid" you mention cover the entire scan area?
I tried a prototype light lid for a Hewlett-Packard 4c scanner with decent results - not print quality, but better than a typical proof-sheet.
I scanned a couple of negatives at max optical(600x600) and got ~4.5MB files. Good enough for a decent 4x5 or so print, but not much bigger - it gets pretty fuzzy.
A flatbed is OK for proofing but you'll need more scanning resolution for prints from 35mm negatives.