Hmm, you don't wanna get me started on Flash websites, so I'll just let some other guys do the talking for me to avoid you not liking me very much, lol
Crap to ignore:
Flash @ CLOUD PANIC
Flash is a fun tool for graphic design and animation, it's not a web design tool. But if you really wanted to you could also program your upload modules in action script and use flash.
What you are looking for is actually pretty complex. Because you need a backend that can handle user accounts and user uploaded content. This is not something you will be able to do yourself, that is serious programming. Just the security requirements need a professional or a professional product. You cannot just give people access to a server. Their access has to be limited and protected, the data they leave about themselves or which they upload needs to be secured protected.
This is why WordPress was suggested to you. It has a lot of what you require integrated already and because it is very popular it's probably safe to say that security updates are fairly frequent. WordPress is not just a blog templating system it's gone far beyond that and it is by now a full content management system. Having said that I'm not sure it would be my first choice for a user upload community I think it's natively a little too far removed from that.
I'm actually looking at creating something very similar. A place where people can sign up and upload stuff and I'm also not a PHP/CGI/Ajax programmer I subcontract that sort of stuff. But this is a little private project and I just want to do it in my own time so I am at the moment working with:
Adobe Business Catalyst
This can probably satisfy your needs. But it also needs a little studying. I'm just getting started with this.
Depending on what you need you could also use a forum software like the one we're using here. User accounts and uploads are part of most forum scripts these days.
Let me know if this helps you along the way or if you need any further assistance
Cheers
Chris
