That overclocking guide is rather old, as a FYI.
Basically with your level of knowledge I would not recommend to do any overclocking just yet. Neil is correct in saying that any overclocking is not necessarily possible, each chip is different and will have different capabilities.
The Cooler Master V8 is a good heatsink, and definitely money not wasted in my opinion.
If you really want to get started, do lots of reading on it first. Plenty of results in Google searching. And of course, be warned that your in essence on your own. If anything blows up, well you are voiding any parts warranty in the first place...
In my opinion, if you are really keen, just look to do a small overclock so you can understand the basics of it. The E8400 runs at 3GB stock, so try aiming for 3.2GHz and fully test the machine for stability afterward. Leave it there for a few weeks, constantly checking the machine is running perfectly fine and look for any signs of system unresponsiveness or other errors.