Anyone have experience of running Drupal 6 and 7 at same time?

Hi,

We are new to the world of Drupal and have several projects we wish to use the platform to deliver. Trying to get to grips with the various modules/distributions it seems to me that we would need Drupal 6 and 7 to satisfy our current requirements! 

Wondered if anyone had experience of running such a set up in an enterprise environment or whether I was completely barking!

Cheers,

Spence