The SQL Server 2005 Advisor is a free download available at www.microsoft.com/sql and is also available on the install media. The purpose of this utility is to let the user know about issues that will need to be addressed when upgrading from 2000 or 7.0. I always tell people to go to the website to get the "freshest" version of this tool. The latest one is dated Jan14, 2006. From my experience with customers, it does a gret job finding all of the issues. Everyone gets the "Disclaimer" message when viewing the Upgrade Advisor report. This message basically says that MSFT has tried to find every issue for you, but there is no guarantee that all issues will be found using this tool. Lawyers get into everything.
Antoher tool that has been around for a while and is still a good thing to do is to download the SQL Server Best Practices Analyzer. Run this tool against your 2000 databases to see where you can improve your environment before upgrading. Perhaps there is a practice that is employed in your environment which is really a "worst practice". I recently had a customer who prefixed all of their stored procedures with "sp_". This is definitely a "worst practice" and would be identified for BPA as such. This customer thought it was a "Best Practice". Download and check it out to see how your environment compares. You can even add your own rules like naming conventions.