Right now I have a 2000 M Roadster, but always thought about someday selling it and getting a boxster. How do you think these two compare....pro/cons?

 

They are both great cars. I'd suggest getting a copy of one of the several comparison tests done back in 2000 or so of the two you are considering. Car & Driver and Road &Track both did M Roadster vs. Boxster comparisons and they will be a scomprehensive as anything.