"Search" doesn't find content in .eml files

I'm using Thunderbird email and I'm evaluating software for archiving my emails. The software I'm interested in will output a series of .eml files, and TB will pull each email up when I double-click on the filename. Now if I could only figure out a way to search the files, I think the software would work for me.

The problem is that when I use "search" (WinXP) and specify the folder that the .eml files are in, I never find the search text I'm looking for - I know that messages exist in the folder with the search text, but the only hit I can get is on text that's in the message's HEADER, not in the BODY - Any idea why this isn't working the way I would have expected?

I've looked at a number of desktop search programs (Google, WDS, Yahoo, etc), but they require that they maintain an index - I don't want that kind of overhead, just want to search a folder on rare occasions (may be on a CD, for example) and I'm willing to live with a bit slower search due to a lack of an index. The standard Windows "Search" function would be fine if it would only find the search text in the body of the message.