The passage on my DELL Inspiron 1720 (Dual Core 2.1 Ghz - GeForce 8600M GT - Windows 7 32-bit) of RAM to 2x1GB 2x2GB DDR2 makes my reactive system more than ever before. My PC does not train, and heats less than before - probably the hard disk that is less busy than before in virtual memory.
The RAM was immediately recognized by my PC at boot, no manipulation to do.
Be careful though: if your OS is 32-bit, it can not fully exploit the 4 GB of RAM. Depending on your OS (XP, Vista, 7 ...) you can not use that 2.75 to 3.5 GB of RAM. For example, at home, I am restrained to 3.5 GB of RAM. You will therefore eventually need to pass your 64-bit operating system if you want to use all of your 4GB of RAM, which requires a complete reinstall of your OS.