I use Audacity to download from the R1 and then save it as a wav file.
the file should already be a wav file on the R1. Instead of using audacity to download the file from the r1, try just copying the file from the r1 to your computer. When you hook up the R1 it should act as a drive under my computer, from there just copy the file over and then try opening it Sound Forge.
I use 24bit files in Sound Forge all the time, so I don't think thats your problem.
Can you record a 16bit file on the R1 or does it only do 24bit? If you're just making ringtones, it seems like 24bit would be overkill.