booting from HD2

Hold down the OPTION/Alt key right after the startup chime sounds and select the volume you want to boot from.
Or go to System Preferences > Startup Disk.

zoran said:

and how do i set that disk up with OSX so i can work with it?

Click to expand...

You mean, you have a second HDD, but there is no OS installed onto it?
If so, use CarbonCopyCloner to clone your existing OS onto that HDD or use the grey Restore CD, that came with your Mac, or the Retail DVD you might have of Leopard, to install Mac OS X onto that second HDD.

Or am I misunderstanding you?

zoran said:

I dont want to clone the OS already installed cause my mac is not working so good with that configuration, i want to make a clean installation so i can set all things right from the beggining

Click to expand...

Then insert your Restore or Retail CD/DVD containing the Mac OS X installer and perform an installation and choose the other HDD as target. If it does not show up as option to install to, format it properly like in the guide shown below.

zoran said:

ok i will check it, and by the way, once i set it up will be able to see the original HD so i will be able to transfer my files?

Click to expand...

Yes.
A formatted HDD with data is visible just like a formatted HDD with an OS, which is only data too, in Finder.