"Cannot open file C:\Users\SWIM\Documents\GOG.comDownloads\witcher\setup_the_witcher_enhanced_edition-1.bin."

What does this mean? Everything I have is up to date, I've checked every driver and every self help and nothing is wrong. I just spent hours waiting for this to download using the gog.com downloader beta.

Do I have to wait hours more to download through the browser?

Check the downloader folder to see what .bin files are missing. If it's just the 'setup_the_witcher_enhanced_edition-1.bin missing download it manually and place it in the downloader folder.

Ok it's there, but in a billion different pieces. Everything is '.bin.chunkN' where N is a different number from 1 to 200.

I assume those are supposed to be combined? Can I do that manually?

I have no idea mate, sorry.

Downlaoding that one file manually trough your browser and tossing it in that folder will likely solve the issue though, asuming that bin file is the only one that failed to combine properly.