The heatsinks that are shipped with brand name comps are usually bottom of the range, basic jobbies (I know, I have a box of them). You can go to
here and see a range of them, and they are not too difficult to fit. However, you do need some thermal compound, thermal compound cleaner and a lint free cloth (I use the ones you get with glasses from Specsavers). This only applies to desktops of course, for laptops you just have to sit them on something cold - like the missus.