Needed: Knowledgebase/Support system with visitor-side and operator-side feature

We are a service company who wants our clients to “self-help” on the website but also want our employees to have a training and operational tool to resolve service issues…

Think Dell – you have a computer problem… you use the knowledgebase and try published solutions 1, 2 and 3 then call customer support staff who has extra options 4, 5 and 6…

Is there any knowledgebase support type tool that fits the bill?

I SO appreciate any responses.