Discussion Groups / English Usage / January 2004

I always seem to struggle with commas...

I know commas should be used to separate introductory phrases from the
main body of the sentence, but it's sometimes not clear to me when a
phrase is introductory or not.  For instance, which of these is
correct?

Installing XYZ
---------------
1. Before installing XYZ, ensure your computer meets the following
system requirements:

2.  Before installing XYZ ensure your computer meets the following
system requirements:

or maybe this is better:

Ensure your computer meets the following system requirements before
installing XYZ:

Can anyone advise?

Rick