Hi Roy
If you aim for around 320 to 400 pixels width (height at whatever it becomes when you set the width to the aforementioned) you should be fine. A file size of 30-60k would be about right.
One of the best pieces of software for resizing massive photo's is the awkwardly named but free Irfanview -
www.irfanview.com - not a large download and all you do is open the original image, just select Image -> Resize/resample from the menu and set the width to the number of pixels described some moments ago.
Hope that helps
Scunner
Free advice to those who cross his palm with plain bounties