Dual to Quad Core Upgrade For Dell E521? [SOLVED]

I am planning on upgrading my Dell e521 to a new processor. Currently it is an AMD AthlonX2 5400. I have the following questions before I make a purchase.

1.Can I upgrade it to a Tri or Quad Core processor or do I have to stick with the AthlonX2 series?

2. I've heard that thermal paste isn't always necessary and in some cases can be counter-productive. Do I have to use it and, if I do, should I use silver paste or a thermal pad?

3. The heat sink in my E521 is HUGE (about 4 inches cube). Would it be better to use that instead of the fan/heat sink that comes with the processor (I imagine it is).

Thanks in advance for serious replies!

[SOLVED]

The E521 does not support anything higher than a dual core processor. I plan on getting a CPU - Motherboard Combo to do my upgrade. Thanks for your replies!

Dell never sold the e521 with a triple or quad core - so I expect the BIOS will not support them...

http://www.dell.com/content/produc [...] b=specstab

Sorry but you are stuck with the system as is - I would not recommend you try a CPU upgrade as I do not expect it to work / be BIOS suported...

1. Don't know.

2. Use thermal grease. Much better than thermal pads.

3. Probably the heat sink is better.