there is no need to mount your negatives to slides, at least not if you're willing to buy a decent negative scanner.
you do NOT generally want to use a common flatbed scanner to scan negatives. at least, this has been my experience to date. even with their negative adapters, the resolution just isnt good enough. i havent used or tried every flatbed scanner out there, so take that last statement with a grain of salt. there may well be some decent ones... i just havent seen one yet.
you can find decent scanners that will do the normal 35 mm film and slides, but also medium and large format including transparencies up to full standard page sizes. i'd suggest starting at someplace like the Epson web site and looking at their scanners.
when looking for a negative scanner you want resolution, the higher the better. i wouldnt go with anything less than 1800 dpi. a normal flatbed scanner may have a high resolution scan for normal prints, but when they do negatives, something changes, and i'm not quite sure why. so, make sure you check out their specs for the negatives and not just for prints.
here's an Epson page that has one scanner that looks like it might suit:
http://www.epson.com/cgi-bin/Store/c...o&oid=49164280
ok, that was a horrible paste.
the point is, there are scanners that will work, and there are scanners that might make a dog's breakfast of things. do some homework on this. a simple google search on 'negative scanners' will turn up some good leads.
you shld also be able to find some links to services that could do what you want. compare the service price to the scanner price and bear in mind you have 1500 negatives times the service price per negative. so, even if you find one that charges only 30 cents per negative, 1500 times .30 is $450.00. that might well buy you a pretty decent scanner that you now own.
Craig
edit: another option is a light box and a good digital camera with a macro lens.