If you have access to an Exchange 2007 SP1 build, DO NOT install it into your production environment. Also realize that Exchange 2007 SP1 will extend your Active Directory schema.
Just to give you a little bit more information: with our TAP customers, we go through a very specific process to make sure that there are no issues when Beta builds of Exchange are joined into production. Exchange 2007 SP1 is Beta code. As such, it has not been extensively tested in all possible configurations and results of installing it into the existing Organization can lead to unexpected results.
We want to strike a balance between releasing early builds so that our customers can see the product and give us feedback and ensuring that our customers have a good experience with the product. When our instructions about an early build being for testing only are ignored, customers can have a bad experience and it makes it harder for us to decide to release early builds because we don't want those situations to happen.
What you of course can do, is install Exchange 2007 SP1 in the lab and test it there... you can test coexistence too (meaning, having Exchange 2003 servers in the same Org) but this should be in your labs only. We also provided ability to test-drive Exchange 2007 in other ways.
Please be patient. We know that many are waiting for their favorite SP1 features, but it is not the time yet to roll this into production!