Yes, you can use any of the Poser figures in P7 - several folders worth of previous figures are included in Poser 7. 

As for going from P6 to P7, can't really say there, I went straight from P5 to P7. But 7 does have some new features that are well worth the upgrade.

Hey! His nose is dry! ... Someone should lick it,  just in case. - Diego