PC upgrade, any advice?

Well, this machine is a somewhat old (could be worse) Emachine (XD, yes I know) and as you can guess, it needs an upgrade.
I believe this is our motherboard:

Motherboard
Compatible processors

And these are a few CPUs that I might like:
CPU1
CPU2
CPU3

As far as I’ve read, those processors are compatible, is that correct?
I’ve never ever replaced a CPU before, so is there any extra factors I need to be aware of? (I know about the thermal grease, and I ordered some antistatic gloves too) :smiley:
Our current CPU is single core, the processors I want are duel core, will I have to make any BIOS changes or anything like that?
When there’s a 2 Gigahertz processor, but it’s duel core, does that mean it has a total of 4 Gigahertz processing power?
Is there anything else I should know about changing my CPU?
Thank you very much for your time!

Really, people calling it “duel core” [sic] should not open a PC before they have read more on the topic.
I tell you that from experience.

XD Dual core? So I messed up one letter, XD.
Will all those processors be an improvement over the current 2.01 GHz (single chip) processor we have now? And are they all compatible?

ROFL duel core, I realized what I was saying XD.
I also wanna get some RAM, any suggestions about that?