I use a freebie little program called Photo Resizer lite, it does just what you want nicely and the pics still come out ok, there is a Pro version available but you have to pay for that.
I have used it many times to upload pics up onto here and other groups
http://www.showyourphotos.com/Bonus.html
check the link and you will find both versions there, it is a very simple program to use.
Regards..........Mark