Hi -- I have a few tips to add, hopefully they will help regardless of the overall system or SW you use:
1) I like to make sure the designers name is in the file name so I can mix & match elements easily -- here is a great tool to help with that so you can do 'batch' renaming -- ReNamer -- FREE and available at
http://www.redbrick.dcu.ie/~den4b/Projects/. Probably some other good renaming tools out there, too.
2) if you make sure the file name includes the type of element, that will help in searching too (i.e. Kathryn_Balint_buttons.png)
3) I like to rename the preview images with ! as the first character so they will always be at the top of the list ( i.e., !kitpreview.jpg)
4) I print a contact sheet of my favorite designers kits so I have a quick visual reference of the kits I've purchased -- PSE has a built-in function to do this. I'm sure other SW apps do too..
FINALLY -- for MOST graphics file formats, they usually do not get compressed very much by zipping (that is, the .zip file is usually pretty much the same size as the total size of all the unzipped files). SO -- when I burn my elements to CD, I leave them UNCOMPRESSED or UNZIPPED so I can view the thumbnails more easily.