It depends on what kind of server your website will be hosted.
If it's a Windooz server, you'd better stick to asp scripts
If it's an Apache-like server, php is the best you can get.
Scripts for uploading pictures or other kind of documents require write access on the server. Be sure your host allows you do CHMOD on folders.
Some basic security to protect the upload pages would come in handy.
If you don't understand a word of this, read the manuals of the scripts very thourough!
The best website for finding ready-made scripts is www.hotscripts.com (I'm not affiliated in any way)
There's one gallery script I like particularly: http://coppermine.sf.net/
If you have any further questions, don't pm me. If you happen to know my email address, please destroy it now