Tracking Vague Requirements for Web Development (Tools/Techniques?)

So i've been placed in a position at starting a QA Dept. at a Web Development Company. It's mainly a Rails shop and I came from QA departments where requirements are strictly defined (A needs to do B and C expects D...etc...)

However at this Web based company (and i'd imagine other smaller web-dev companies) requirements are really strictly defined and aren't kept in any specific tool and tracked in detail. As in the requirements are more coming from the customer of what they are "looking" for and then slices are taken and created based off those.

I see this as a good and bad thing, it allows the spec/requirements to change and be flexible without much changing of anything spec wise...but actually tracking these for testing becomes a problem. I don't need anything super specific...but I need "something".

So I'm looking for a way/tool to be able to track high level requirements obtained from a customer, and then (ideally) place my "issues" relating to these requirements in some sort of trackable way, but I haven't found anything flexible enough to allow this (then again I'm new to manning a QA dept.)

Does anything come to mind for doing this? is there any particular techniques I should keep in mind when doing this? Right now DoneDone is being used for tracking bugs...so perhaps even that could somehow be linked to these specs?

Thanks for your time.