Hello
More RAM is always good, especially on Vista and Windows 7. 4GB would be good for Windows 7 if I run some applications. Furthermore RAM is very cheap these days and an upgrade wouldn’t be expensive.
The part number for one 2GB DDR3-1066 module is PA3676U-1M2G.
By the way: If you want to upgrade your OS you can use the Windows Anytime Upgrade. So you can upgrade without reinstalling.
