The "sweet spot" for memory for a 32-bit Windows 7 system is 4GB of RAM. A 32-bit system will only be able to use about 3.4GB of that RAM so some of it will be wasted.
With 4GB of RAM, your system would run somewhat faster and be able to handle more tasks simultaneously but don't expect miracles since you only have a Pentium Dual Core processor.
You should be able to find the RAM you need by going to crucial.com and using their system scanner to determine which RAM your system needs.