I guess I'm a confused person!
i was talking about project properties, but it also worried me thinking that i need to have 2 separate versions of hte program for office 2003 and office 2007 (connection strings for different versions of Excel seem different anyways). Let me rephrase the question.

Is there a way to
1) determine the MS Office version at runtime to use the correct connection string.
2) would i need to load the correct version of office references (the one we add to project-> add reference) at runtime? If i already have added Office 2007 references to my project, would my compiled program work fine on a machine running Office 2003?