Which upload did you try ? The "normal" one, or Uploader + ?
Anyway in both cases of course images are limited in size and weight. I don't think it is really possible to make the site itself process the conversion, as it can increase too much the CPU time of the server, from a requirement by the site. Your internet provider could tell you you're asking too much from the server.

EDIT :
And, mainly, you cannot allow users to upload on your gallery a set of 10 images of 5 Mb each ! Even non considering the upload time -- in the US I guess your average bandwith is better than here --, it is a lot of space and ressources used for some work that indeed should be done before the upload.

Well, I'm looking for a method of allowing users to easily upload a set of pictures. These users would be members of our church who want to post on our web site pics of various church events. Many of them would not be real "power users".

Thanks,
Steve

It depends how much you trust this user. If you trust the user (family member for instance), you can give him/her administration level and let him/her use extension:270. If you don't trust the user, then you have to use the [wiki] Upload by users.