Is there any conflict?
A colleague of mine (think he has an account on here as dcraggs now) has got them both running on the same machine just fine, I believe.
Certainly would be a huge own-goal from Embarcadero if installing D2009 broke an already-installed D2007, given the way that the components and DCUs are not compatible - I suspect a fair number of people will need to have both around for a while (some of us still need D5 and D7 too!)