High rise in SQL Server CPU after adding a DB
Read this article from Paul Randal on wait stats. You find what sql server is waiting on using the sys.dm_os_wait_stats DMV(Data Management View). It sounds like it MIGHT be a query plan change between versions. But there are a lot of things it could be. Could be storage too. Wait stats should help. Check to see if the MAXDOP setting was different between the versions if possible, you stated the original server died, but not sure if you have the server config saved in a repository for DR purposes. If it's a highly transactional system, parallelism can slow you down. Make sure you know what you are doing before making any changes to MAXDOP.
Also check this article from this thread on SO , it will help you find the worst performing queries. And for more information, check Brent Ozar's Blitz scipt
Hope this helps, Good luck.
Chris