i was reading the photoshop 6 post and i know alot of people can't afford to buy it. I have photoshop but i rarely use it to make thumbs because it takes so long to launch and i can't do as much multi-tasking when it's running.
I usually use a piece of free ware from
http://www.tucows.com/ called irfran view.i use irfran view's batch conversion to make thumbs. i just make them 100 pix in width and i don't bother cropping it square. just takes twice as long if i crop but you can do it if you want. on an 800x600 page you can fit 7 thumbs across without distortion. then i batch convert the files to 50% with 256 colors. i can also batch convert the names of my thumbs so that i don't have to rename each thumb by hand.
it's a great piece of freeware and it doesn't use alot of system resources so you can run other apps at the same time. it's also good pictureviewer.