Make sure your images are optimized to the right size (400 x 300) for faster uploading. Anything larger than that is a huge file and gobbles up resources (yours) while uploading and can cause the process to be kicked out.
I use a free software...called Irfanview.
Download Irfanview
Auctiva member, biscuit just posted this great looking software for photo manipulation
FastStone Image Viewer
I haven't tried it yet..but biscuit has great advice, so I trust his judgement.
Best of Luck,
Donna