Search engine/ directory

I'd like to build up a web directory targeting specific sectors - and encourage visitors to add their own sites to it - as a key method of building the directory. The site should appear as a branded search engine, clean, minimalist site - options for visitors to download a customised toolbar or search widgets for their own sites.
I am aware of various open source scripts around but do not have the technical expertise to do this. Please advise on this and offer some bids.