This may seem a little funky, and it is somewhat dependant on what you want to allow as machine and user names. But this should give you something to work with.

my ( $date, $activity, $machine, $company ) = $_ =~
    m/^(.+(?:AM|PM))
       \|\d\|
       (.+)
       \sfor\s
       ([\w\d-]+@[\w\d.-])
       \s.+\bby\s
       ([\w\d])
       [^\w\d]+$
     /x;
[download]

I used the /x modifier to allow whitespace within the RE, so that I could group it in segments that each accomplish a different portion of the match. You probably ought to also have a look at perlre and perlretut, as well as perlfaq6. They will go a long way toward giving you a good comfort level with RE's.