1-Do i need a specific computer requirments?, the computer I found its processor is "intel pentium 4 3.2 ghz", is that enough for a Linux OS to work properly?
No, you can run Linux on virtually any hardware (almost). You can run Linux on a 300MHz processor, that's more than 10 times below 3.2GHz, so yes, you can run Linux
What bugs most people, is proper hardware support, but if you use Ubuntu and use their website, their forums and Google, you should be able to make most of your hardware function in case any of it doesn't work right out of the box. (Depends on how new your computer is and how common your hardware is.)
If you need e.g., wireless drivers, and it seems like there's none for Linux, try out 'ndiswrapper'.
2- I am an absolute beginner, so i dont really know which Lunix to get (redhat, ubuntu...etc), I am going to be writing shells and get fimiliar with Linux commands thats for first, afterwards will be doing some pentesting and programming in general, so what version of Linux do you suggest and why? if possible could you support me with a download link for the version you suggested?
It's Linux, not
Lunix. (The latter is only used in jokes made by hackers.) I would recommend you use Ubuntu for starters, but you can use Fedora too (based on Redhat), or Mandriva. Most people go with Ubuntu or Fedora though. I don't recommend you choose something like Gentoo or Slackware yet.
BackTrack is based on Ubuntu in case you don't know.
The newest version of Ubuntu will do.
If you want to run it in a Virtual Machine, you can do so easily too, by downloading e.g., VirtualBox or whatever you have or prefer, and then run the ISO in that and install it into the VM (Virtual Machine), just like a normal CD.