That Opteron will not work.
Maximum TDP is 89 watt.
And the Opteron is actually on a different socket.
That Opteron is socket F compared to your Athlon 64 X2 which is socket AM2.
That Opteron will not work on your motherboard.
You can only install Sempron, Athlon 64 and Athlon 64 X2.
I would suggest upgrading the power supply and installing a dedicated graphics card to improve your PC performance.
Once the cpu is installed put the thermal paste size like a grain of rice on top of the cpu. http://www.gophermods.com/images/gm_paste_applied.jpg
Or you can use a credit card to spread the thermal paste evenly across the CPU area.
Once done install the heatsink back to it's original position.