In Team Build 2005, the "definition" of the build was the same as the TfsBuild.proj file. However, in 2008, we changed this so that the TfsBuild.proj only held some of the information for the build. The rest of the information (like retention policies, workspace definition, and triggers) were all stored in the build database. 2008 even allows two different Build Definitions to share the same TfsBuild.proj file.
Unfortunately, due to this diversion of "definition" and source control file (TfsBuild.proj), users have found it difficult to easily get to the TfsBuild.proj file from the UI. Okay, you can find it, but you have to follow this procedure:
1) open the associated definition from team explorer
2) go to the project file tab
3) write down the server path
4) open Source Control Explorer
5) Navigate to the right server path
6) look for the file TfsBuild.proj
Well, in 2008 SP1, you don't have to do all that work any more. Simply right click on the definition in team explorer and choose "View Configuration Folder". This menu item will do all the of the above for you. In future versions, we may even dream of world without TfsBuild.proj files 😮
For more information on all the new features in Team Foundation Server 2008 SP1, see bharry's blog about them.