I like the microsoft office picture manager (I think it came with microsoft word) it has predefined sizes that you can just choose from.
document large 1024 x 768
document small 800 x 600
web large 640 x 480
web small 448 x 336
e-mail large 314 x 235
e-mail small 160 x 160
or you can choose custom w x h or percentage of original
It's so easy even I figured it out by myself
DQ