I edit a computer user group newsletter, and lead a MS Windows Freeware SIG (Special Interest Group). I would like to find cartoons to use in the newsletter and for slide presentations, that carry Creative Commons attribution licensing.
Feel free to use my cartoons for your newsletter. The subject tags are at the bottom of the blog.... you'll even find some Apple related cartoons there.
I guess you could try using Compfight to search for the kind of toons you are looking for. You will have to very careful with your keywords though. For example, there's a better chance of you getting hits for "Microsoft Toons" than "Windows Toons". Play around with the terms till you get it right.
Also, Google Images Advanced Search might also be a good place to start with.