How to clear memory in 2.3.4 like I did in 2.2.1
Your previous Task Manager was a Samsung addition, and not part of Android itself.

In 2.3 onwards there's a very similar and memory usage listing. If you go into Settings, then into Applications and click the "Running Services" option, it should show you everything that's running along with how much memory it's using. There's also a small graph at the bottom showing RAM used vs RAM free.