Are you using Infra view ? I don't use it myself but
a good size is 460 pixels
there is another very easy program also ...I found it's great for beginners ...
http://bluefive.pair.com/free95.htm
Scroll to PixResizer……Download the program..it’s really small and very easy to install –
Depending on the size of your image you just have to click ONE SIZE (USUALLY 50%) or 400 Pixels and it resizes it for you... The whole program is THIS below - only one window - and very easy - 2 clicks and you're done.