isntallation problem

Hi All, I'm new to ubuntu. migrated to this after reading an article at which mentioned that ubuntu is the most popular destro for desktop i  downloaded the  iso image and burned it on a  CD, but i'm unable to boot from this CD. it goes to a menu driven program where i am asked to enter my choice. selecting installation tab fails and gives error message. My desktop has folllowing configuration: processor: AMD athelon 3000 RAM: 256 MB Hard disk: 8O GB please let me know if you need more details. Thanks, mxms