Upgrading a Dell Dimension 4600i

Hi there this is my first time posting on here so please bear with me.
Basically i'm looking to upgrade my Dell dimension 4600i.
The current specs are:

2GB RAM

Intel Pentium 4 CPU 3.06GHz (2 CPUs)

Nividia GeForce4 MX 440 with AGP8X Graphics card 64MB Approx Memory.

I believe it has a 250W Power supply.

I mainly use this for World of Warcraft, i'm looking to upgrade to improve my World of Warcraft game performance.

As far as i'm aware my graphics card is awful and needs an upgrade.
Please guide me with advice on what i should upgrade to.

Thanks

Ok thanks for the help. If i upgrade will i notice a big difference in gameplay from what i currently have and will it increase my FPS?

Yes you will, I had a MX420 before I upgraded to a HD3650 (Actually same HIS card you linked ) And it performs way better in games and various things (movies, HD).