Thrilled to find you guys! Another newbie question

Alright, I've read all the Newbie info at the top (THANK YOU PsychDoc and Dave) and looked at the letters in an attempt to avoid embarrassing myself by asking a really obvious question, and I'm trying to have patience with my general ignorance here, but I have one question I haven't found the answer to yet. I hope you can help!

I'm finally making credit repair a priority and am tackling things one at a time, and you guys would probably laugh if you saw how little I actually OWE to clean it up. Most of the entries on my report are chargeoffs from 4 or 5 years ago and most of them are less than $50, lol. Everything on the report is accurate and because it's really not that much money I'm just paying them off rather than fighting them. I have 2 larger ones ($200 and $400) that I'm requesting 50% settlements on and will pay as I'm able.

But there's this one creditor that just burns my everloving BUTT, and I'd like your help on how to approach it.

In mid 02 I opened a Citibank card with the retailer Children's Place to get a stupid 10% discount on a $20 purchase. I even paid half of the purchase with cash, so I charged a total of $10. I was pregnant at the time and had my son right around the time when the bill was due, and totally forgot about it. A late charge was tacked on of course, and the next bill was for $40. I actually PAID that bill, but my payment was late (again) and by then the balance was $70 so even after my $40 payment I still owed $30. I called and talked to Citibank, whined and complained, etc, and got nowhere. At that point I got so frustrated I just ignored it (can you say STUPID?) and sure enough the late fees kept accruing more late fees until somehow my balance got to THREE HUNDRED AND FORTY SEVEN FLIPPING DOLLARS!!!!!!!!! I've been kicking myself ever since for not doing something about it at that time, trust me, but everyone here probably knows that 20/20 hindsight doesn't really fix your credit issues, lol.

Citibank has been aggressively attempting to collect on this debt for SIX YEARS. It's been to more collection agencies than I care to think about, and was recently placed with a new one. They've offered me a 50% settlement, but I just can't bring myself to pay it. I've paid this stupid debt and I can't see paying a couple of hundred dollars for what was originally a $10 charge.

Can you give me suggestions on how to begin? I presume a validation letter and then a dispute, but I would like any info you have about whether this is a legit debt or not and if the fact that it's 100% late fees helps me any. Thanks so much!