Help with deleteing 2 partitions on hard driv

Hello,
I am trying to format my hard drive. It has become very slow. I have the install cd for Vista and I restarted the computer with it in the dvd-rom. I deleted the 2 partitions that was on the hard drive and now it will not let me format . There are 2 os on my computer and i want to format the drive and start over. I have a Sony Vaio Laptop, 160gb hard drive, 512 memory, with 32-bit Vista Home Basic CD. How do I format or delete the drive since the oppition for delete and format is not a button? Do I do a new and what size partition should I put on it?