Well, yes, you'll need ASP or PHP.
Really, what you want is relatively simple. But your kind of approaching it from the wrong angle.
Do you want to integrate this with the already exsisting user content? What type of database are you using?
If your using a database, then, it's gonna be really simple. But, instead of actually creating a new page for every submission on your server, it'd be better to use a RecordSet filter.
You probably don't know what that is, but, UD4 can do everything you want it to - it can be tricky at first - but you'll get used to it.
Seen as your coming from flash - i'd recomend
PHP.