Depends on your computer- we recently got a new one with Vista so i've had to re-learn!
Usually you open the pic, right click on it and look in properties- it'll tell you the pic is 437k or summat like that.
The next bit is where each pc seems to be different... on ours we click 'open with microsoft picture manager', then theres an option to resize by percentage of original size, then save and it's done. Needs to be less than 256k if i remember right? (that's actually about 75% of a 400-ish pic)
My work laptop is XP. It's a similar process but they give everything different names and put 'em in different places
