Compare the features and Guide number.
I can't say anything based on personal knowledge of those models. I have a Canon 380EX for my EOS Elan film camera. I haven't used it a lot, but the ability to bounce the flash is nice, and it has a much larger range than a built-in flash.
Modern flash units work with the camera's RedEyeReduction circuitry. Older ones, don't. If that's important to you, compare them carefully.
A review of the SB-24 is here -
http://www.stahlbran...camera/sb-24.html
A review of the SB-600 is here -
http://www.kenrockwe...m/nikon/sb600.htm
The Guide number gives information on its effective range at ISO 100 for a given aperture. It's too early in the morning for me to figure out how to compare the Guide numbers on those 2 pages. :-/
B&H has a variety of used Nikon flashes, including a SB-600 for $170. Their prices start at $28. Maybe give them a look?
http://www.bhphotovi...bmit=Submit+Query B&H are good folks, and they'll buy used equipment for reasonable prices IME.
I hope this helps a little. Good luck!
Cheers,
Scott.