500 Internal Server Error when importing high resolution images

I have a 1and1 shared server account running Drupal 5.x, and when I upload images that are the size of 1600x1200 the page immediately goes to a 500 internal sever error. This has nothing to do with -file- size, because the image could be smaller than a 1024x768 image in file size and it will still go to the server error (of course this means an image that is smaller in resolution, but with a larger file size successfully imports). I've upgraded to the Dev build and the same issue occurs (and I lose all of my images in the node system - not file system though). Any quick fixes for this? It has to do with image resizing obviously, I've done everything short of calling my webhost when it comes to tweaking. That includes increasing memory, adding .htaccess command " RewriteBase /". I have uploaded images that were larger than this to another Drupal site running 6.x and the issue does not occur (both on the same server)...I've also used other software such as Photoplog that resizes images...and they too worked successfully...but importing...or uploading a high resolution image to this build always results in a server error.