before spending a lot of money to upgrade your notebooks ram check the price difference between DDR2 and DDR3 since if you need a lot of ram it might be cheaper to replace your DDR2 notebook with a new DDR3 notebook !
for example on 13 may 13 the prices were
- 4G DDR2 £55 http://goo.gl/g26xT
- 8G DDR3 £54 http://goo.gl/1Xo8E
ie DDR2 is TWICE as expensive as DDR3