I just replaced my air filter at 24k miles and have a question. There are two tabs on the upper cover of the air box. There are also 2 holes on the lower box. My questions is this: are the tabs supposed to go OVER the two holes, or are they supposed to go INTO them? It seems like it could go in, but I am having trouble doing this. Just want to make sure so I don't have any unwanted leaks.

Here is a picture:

http://img.photobucket.com/albums/v146/ezandfast/airfilter.jpg

The manual seems to suggest that they just go over the holes (they used "align"), but I just want to be sure nonetheless. :p

The tabs must go into the slots at the bottom. If they don't the airbox will not be fully closed and sealed.
It's easier to get them in place if you put the filter panel in the top cover while closing it, instead of putting it in the bottom part.
Failure to properly close the airbox can result in increased intake noise, unfiltered air entering the intake, and can sometimes cause a P0171 lean condition CEL.

As always, thanks Mulder! Shoot, I had the tabs over the hole instead of into it for a few hundred miles. Hope I didn't kill anything :(

On a sidenote: Is a lean condition ALWAYS accompanied byknocking/pining (whatever the correct term is for the bb in a tin can sound)? I have had a few detonation instances in 4th gear WOT, but vanished the next day. Perhaps it is because of the airbox.

Hm, that's not good. Any knock, especially when it's audible, is a bad thing. Yes it's possible that the loose cover had something to do with it, although there are other possibilities such as bad fuel. You might also take a look around in the 2.5 Turbo forum, I recall some older threads discussing pinging on 04 STi's.
A lean condition will not necessarily result in knock, but it does make it much more likely which is why running lean can be dangerous.

Mulder, Thank you very much for the tip about putting the filter in the top cover! I was putting it on the bottom and no matter what, I could not get the tabs into the hole. It took literally 5 seconds to seat the tabs in the hole with your method!

Muchos, muchos gracias! :D

Yeah, that one should be in the manual. :)