From using a few different Umax scanners (1200S, 
2400S, 3400U), here's a little of what I've found 
so far:

* Whatever methods are used within the VistaScan 
drivers or scanner hardware to resize are pretty 
bad -- if you resize, you're best to do it in a 
program like Photoshop or PaintShop Pro

* I found I had good results in PaintShop Pro if 
I did the following:
1. Scan at 4x the resolution you want
2. Blur image (or soften, can't remember which)
2. Resample in PSP to 50% (what I used for my 
larger detail images)
3. Resample to 50% again for thumbnails

I might have done a sharpen image after step 3, 
but I can't remember for sure.

* On the errors with 48-bit, I found that 
whenever I'd tried to scan at anything larger 
than 32-bit, it would only work if I were 
scanning into Photoshop -- scanning to file 
and/or scannning into PSP would tend to crash 
like you'd described