As you can see (via my nice MS Paint writing) the new fan is 80 by 25 millimetres. You can also see that it is mounted on top. I think little metal thing is a real nice touch, don't you?

The old fan was in the back. It was 40 by 10 millimetres. Far inferior to the monster that's on there now. I taped over the hole since the new fan is near the back, that way any air coming into the case will have to rush by the hard drive before being blown out. Clever, eh?

Here I show that I've taken the front cover off. This provides exponentially greater air flow. If you look closely at the bottom of the case, you can see the pin prick size holes that the air used to flow through.

All in all, it was a pain in the butt and a considerable amount of labour (before my friend lent me his dremmel that is), but I'm quite proud of it. And my hard drive now runs VERY cool.
Project costs:
Existing hard drive - $0
Existing enclosure - $0
Fan from defunct computer - $0
my time - $0 (approx. 7 - 10 hours for everything)
Total cost - $0