This is a fairly complicated project. The goal is to make a link-sharing community that resembles almost a combination of [url removed, login to view] and YouTube. The details can get somewhat complicated so feel free to ask questions.
The goal is to allow users to post links to websites that they find interesting on the site. The same link cannot be reposted. The site needs to allow users to choose from any number of categories that are relevant to their links (which can be created/changed by administrators), it would work as such. If a user has a link to a video on the way a computer is built maybe they will be able to check a category called Technology and then within that check a category (a check box [x] type of selection) for Computers. So it would be under Technology > Computers. But then a seperate section could also be made so that they could also define the "goal" of the link, which might be Educational > How-to another may be Video > Youtube. These need to be able to be added/changed by administrators. And the individual link's categories must be editable my administrators.
Each link should be submitted by a user (you must have an account) and there must be a description, categories chosen and the link itself. What should appear when someone is browsing through links is the title (pulled from the site's "<title></title>" tags), description (cut off at a certain number of characters), rating, categories and some method to get to a comments/detailed page about the link. Each link needs to be fully editable by an admin.
There must be a page created with each link (similar to youtube), that allows for users to comment on the link and give it a rating.
There are more, somewhat minor, details left out due to space, please ask if you are interested and wish to learn the rest. Thanks for looking!
You can tell me whatever would work best. I have yet to choose a webhost and can choose it according to your specifications.