[DanaC]

Nah. Just a bonus if you do. The first few series especially were designed as a fresh start for people who hadn't seen the original.

No need to watch the old series (unless you find yourself wanting to after watching the new :p)

Also - the original tended not to story arc quite so much. There'd be a story across a few episodes and then the next set of episodes would be something totally different. There was no real overarching story so it doesn't matter if you'[ve seen none of them, a few of them, or just one of each doctor - the new series is its own beast.