Can anyone recommend a good mbox reader, that lets me access attachments? I'd rather a reader than a regular email program, as I've tried programs without success, but if there's an email program that you've found works very well, I could also try that.

I'm trying to access some old emails from mbox archives, dating to when I used Opera for email (in 2004 - which would have been Opera 7). I know the emails are there as Google Desktop finds them, but it doesn't let me access the attachments.

I imported the files into Opera - it didn't work the first time, and the 2nd time it worked for some emails and not for others. I downloaded Thunderbird, and found I needed an extension - Thunderbird mbox Import/Export extension - to import from mbox files. It asked me to confirm individual mboxes (there are hundreds!) which I did until I realized I was seeing the same files over and over. In the end I found less of the emails I wanted than in Opera.

I tried Mark Lyon's GMail Loader (GML) but got an error:
I installed perl-Mail-MboxParser but can't for the life of me figure out how to run it - I want something that doesn't require me to know what Perl is, otherwise I fear everything I want it to do will require more research.

Any suggestions, preferably for a simple reader?

How about first converting them to Maildir format (for easier searching):

google for : mb2md-3.20.pl

Then, its just a simple matter of doing a mimedecode on a given message file.

I use mutt, it is not what you asked for (it is a full email program), but it does read mbox format and does deal with attachments correctly -- I use it every day. If mutt cannot read/access your mbox, perhaps it is corrupted or does not meet the RFC2822 specification. I found mutt to have a high learning curve, but after spending the time to get it set up it works flawlessly. Good luck!