In one way, introducing Windows 2008 and Windows 7 will interfere with master browser elections in NetBIOS. That being said, this is not an issue for many different reasons.
First, you need to know that master browser selection is based on domain controller status and Windows version (this is where 2008 comes in to play). The PDC emulator will always win master elections no matter what OS level they are at. For broadcast domains where the PDC emulator role is not running, domain controllers will try to become the master. Finally, if no DC is available then the highest Windows version will win the election.
With that being said, very few applications rely on NetBIOS these days. Almost all Microsoft applications and third party applications will resolve through DNS, not NetBIOS.
Additionally, anyone relying on NetBIOS will have WINS deployed on the network. WINS removes the reliance on master browsers and allows NetBIOS to operate across subnets. Windows clients configured with a WINS server will default to H-nodes which means they query WINS before doing a broadcast for name resolution.
Once that is all said and done, if you still needed NetBIOS, did not run WINS and had no domain controllers on a network, introducing Windows 2008 or Windows 7 would allow them to become master browsers on your network. Even if that were the case, Windows 2008 and Windows 7 will happily act as master browsers without any negative effects. If you still didn't want that to occur, then simply set the MaintainServerList and IsDomainMaster to No and False respectively.
/me steps out of time machine...