SQL Server 2008 upgrade advisor tool
The upgrade advisor will work, but you need to make sure to analyze a trace file of activity.  Just pointing it to the database and running it will only analyze the TSQL code stored in the database and not any TSQL code within your application.

In addition to the upgrade advisor, you can run a Profiler trace to capture the events: "Depreciation Final Support" and "Depreciation Announcement".  Both will identify code that will need to be evaluated because of syntax or reference to objects that don't exist in new version.

Check out Books Online for a decription of each of those events: Depreciation Event Category.