404 error performance hit?

By way of tracking users as they travel within my site (there will be several site sections within one .swf, which won't show in the server logs) I am trying to load .swf files that don't actually exist on the server. I could create empty .swf files to match the URL's I call, but this would present me with extra work, now and in the future when the area tags get changed as they inevitably will.

This method seems to work fine for my purposes, the non-existent files show up in the server logs as expected, only with a 404 error obviously. I will be parsing the raw log files so I can easily correct this.

What I am trying to find out, is if returning a 404 error will take more time/processing power than a basic 200? I am wondering if more effort is required in searching for the file in the directory when it doesn't exist. Maybe that sounds silly but I don't know much about the internals of the file system and don't want my application to suffer if this is a bad idea.
Can anyone help please?

I doubt there is any significant difference in processing, for all I know it may be faster to identify a non-existent page. Just guessing.

Thanks for your reply Doug, I hope that might be the case, plus of course there is no file being transmitted over the network which should add up over time.
Cheers