32-bit software/application compatibility in 64-bit Windows 7 issue

I have been using the windows 7 OS for my notebook Compaq presario CQ40-330TU model, and it was working awsome. The 32-bit OS of windows 7 doesn't recognize more than 3 GB of RAM. For which i purchased a fresh 64-bit OS (windows 7). But all the applications/softwares which i have been using on 32-bit OS are now not getting installed on this 64-bit OS. What is the solution to my problem. How can i run 32-bit softwares/applications on 64-bit OS of Windows 7.

My notebook specifications are

Processor Intel Core 2 Duo T6400 @ 2.0 Ghz
Motherboard Mobile intel 4 Series Express chipset family

You have done a double-post. See your post in the other forum section.

I downloaded Picasa and my computer has 32bit and 64 bit for my Windows 7. I just purchased this computer after using a Gateway computer for years. Windows 7 shows Incompatible application for Picasa 3. Would 32 bit solve this problem? Changing 64 bit to 32 bit can this affect my computer in other way?
Another area I have a question on is Adobe Flash Player that does not seem to be compatible for games. Help! Mary