OK. put the ubuntu cd in the drive. boot up the computer bios. set the boot priority to cd first. save the settings then exit. u should boot up into the cd. the instalation is self-explanatory.
Download Ubuntu | Ubuntu go there selcet your download location and then when you see the file has fully downloaded put a blank disk in the drive double click the icon then burn it to disk.
Remove the disk from the drive then turn off your computer then when it restarts press f2 to enter BIOS then select the boot from CD option, ubuntu will take it from there.