Spyware Terminator takes on both of those. The ST program will find and remove a bit more then Ad-Aware 2007 and also places an active guard around the system registry. Even when using the add/remove or Programs+Features seen in Vista ST will prompt to allow or deny any changes. http://www.spywareterminator.com/
Spybot S&D was is a good program as an added protection while somewhat outdated. Both that and Ad-Aware lack the active sheild ST puts inplace similar to a firewall. But the usual advice is being familiar with and not solely counting on any one program by itself entirely.
Ad-Aware occasionally will find something missed by ST. One finds what the other misses seems to be the general rule.
You can have a few programs onhand. I keep Ad-Aware on along with Spyware Terminator and AVG 8.0 for a start. Others are simply backed up and ready to use being stored in custom folders or on a separate drive if needed.