Help installing asterisk now 1.5.0

hI EVERYONE IM NEW TO ASRTERISK AND WANT TO LEARN THE PRODUCT.
I DOWNLOADED THE SOFTWARE AND HAVE EXTRACTED AND BURNT THE PROGRAM TO A DISK AS .ISO
IT PROMPTS ME WITH ENTER CENTOS CD IN THE CD TRAY.
I WOULD OF THOUGHT THE WHOLE PROGRAM I DOWNLOADED WOULD HAVE THIS INFORMATION ON IT.
PLEASE HELP.
CHEERS EDDY