This is how to check if an app pool is running as 32bit or 64bit in IIS 7.
Goto IIS manager -> Application pools -> Select the apppool you want and -> Advanced Settings.
In there there's a setting called enable 32bit apps. If that's true, that means the worker process is forced to run in 32bit. If the setting is false, then the apppool is running in 64bit mode.
Also you can open up task manager and check the w3wp.exe. If it's shown as w3wp*32.exe then its 32bit.