First of all, welcome to the wonderful world of boxing

Second I'm fairly new to multiboxing myself, but I'll try to answer some of your questions.

I heard i need to buy a copy of Synergy and Keyclone? What do those programs do and are there any tutorials to set them up?
If you're gonna run 2 instances on 1 comp you don't need a program like synergy AFAIK, only keyclone will do.

Can my computer handle WoW twice?
Heres a list of my computer:
Windows XP
Intel(R) Pentium(R) 4 CPU 2.80Ghz
Nvidea GeForce 8800 GTS
I think your comp should be able to run 2 instances just fine.
How much RAM do you have?

I would also suggest to take a look at the stickies, there is a lot of info there on how to setup the various programs, macros etc.

I hope this answers some of your questions, and good luck with boxing
A fellow dutchie :P