researching search behaviour

I'm going to be carrying out research into how to rebuild a search engine from scratch for a large University data base. Existing search is slow and cumbersome.

I'll be researching user needs that will try and figure out:

What users are looking for; how they formulate queries; what they do with the results etc.

My question: has anyone got any researching guidelines for specifically search engine user needs?

EDIT There is no quantitative data capture set up. I wish there was.