installing ubuntu on a DELL computer...trouble!

I cannot get Ubuntu to install on a Dell computer. Ubuntu cannot delete both partitions and then install
on that computer. I downloaded the ISO file, put it on a disk. Tried out Ubuntu and liked it. I then tried to install Ubuntu...A few minutes into the install, I'm getting problem messages galore, mainly having to do with deleting all instances of partitions and VISTA,formatting the drive and installing.Any help appreciated.....thanks