Unless there is visble cracking around the dent and the nearby bottom bracket it shloudnt be a concern.

I ahve a similar issue on an old Connondale r500 frame that I still ride for training and it hasnt been an issue in the past 5 years.

The strength of the Down tube with a dent depends on the thickness of the tubing Klein used in the bikes manufacture. I did some research and couldn't find what they were using at the time. It MIGHT be alright, but remember that the DT is the most stressed tube on the bike. I'm concerned with other components that might be damaged...you say it looks like the small ring was the cause of the dent...that means that all sorts of torqueing was involved to make that happen....it may have weakened the bottom bracket and god knows what else...I wouldn't ride it. If it were steel , yeah, but not aluminium.
If you decide to keep it keep a close eye on it. You might also be able to pick up a great used frame and switch over the grouppo.
Good luck!

If its aluminum, any qualified welder should be able to tig a patch over the dent to maintain your frames structural integrity.

I just went and looked at my Trek 2300. Guess what is there right in the proximity of the FD? With the FD in the little ring, there is just enough clearance there to fit a finger tip back there and feel the indentation, its more accessible with the FD in the big ring. It is smooth and sort of vertical oval shaped.

having studied a bit of material science for my Chem E degree I'm not to scared. However, if this dent is enough to cause a structural failure, the bike will simply fold up one day while you ride it. That being said, anything structural is over designed by many factors (i.e. it is 2,3,4,5X as strong as it needs to be). I know many TT bikes out there that have dents and have been raced hard for years. unless the tube folds under the stress of your training rides, or is getting worse, I wouldn't worry about it. Go ride it hard, flex it with whatever force you can put on it with your hands, if nothing happens, race it! If it folds up like an old map, then hang it in your garage and tell stories about the bike that you folded up.

Thanks a lot for all of the responses. I'm just going to keep riding it, and I shouldn't have to worry about the frame folding on 60mph descents in Baton rouge. The biggest hill on my training ride is from the top of the levy to the bottom of the levy.