I was chatting with my buddy and PASS director colleague, Rick Heigis of Scalability Experts.  He was telling me that Scalability Experts developed a tool called the SQL Server Upgrade Assistant that works in conjunctions with Microsoft's Upgrade Advisor to test your application and verify behavior with SQL Server 2005.  The tool has been in use for the past year at Microsoft's ISV Application Compatibility Labs.  There is plenty of info on the link below:

The link is http://www.scalabilityexperts.com/default.asp?action=article&ID=317<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" />

Hope this helps!