It seems actually pretty logical that you would like to search into your email messages, saved in a MOSS 2007 environment. Well, there are third-party companies, selling a .msg iFilter. But... you don't need one. There is a build-in msg iFilter on MOSS 2007. It's just not active be default.
Gavin Adams made a brilliant post to point this out and to deliver a solution how to activate it on your MOSS environment.
Also, it's very easy to do this, just add some values in the registry, do a reboot, do a recrawl and you're all set.
Gavin ends his post by pointing out that he didn't test it with attachments... well, I did today. 
A customer asked for this msg solution, and since I'm not implementing anything without trying it out first, I gave it a testdrive. (Msg files with docx attachments)
Drumrolls... and the results are:
- It crawls content in your msg files (but we already knew that)
- It crawls content in attachments in your msg files (woohoo)
- If you search on content in a attachment, you get the msg file as a result in your search.
I was delighted with the second result, but even more delighted with the last one. It implies that you never get the attachment displayed when you do a search, but you get the parent email, which contains the attachment.
This is very important, because most of the time, the email contains the "context" of the attachment and they shouldn't be handled seperately.
So the build-in msg iFilter is a success. I didn't get to test it in a 64bit environment though, but I suppose (according to Gavin's post) it will work just the same.
Keep on dancing
Tom