HI LORD NITE!
This may be far different than what you wish to achieve but on my board I 'valigned' everything to the top and moved the member's info/authors extra (default at the bottom after the post body) to the top (above the post body). This will prevent any alignment problem that you are experiencing due to various sizes in avatars and sigs...In my opinion it looks nicer too.
I too am in favor of tables so I don't know the exact coding to make the H-Rules work. Anyway, good luck and I hope you'll find a solution that works best for you.
THANKS!
PrimeTime