A general sed question

[David Allen]

I keep bumping up against this, so I thought I'd throw this question out
to those who understand sed better than I do.

What I'm trying to do is to clean up the contents of some files
(/sys/i386/conf/GENERIC would be a good example) to get more readable
diffs.  To that end, I'm trying to use sed to

 - delete commented lines
 - remove inline comments
 - remove trailing spaces and/or tabs
 - delete blank lines, and/or lines containing just spaces and/or tabs
 - expand tabs

Thanks!