Un belivable Vista down graded to XP SP2

Un belivable Hello,
HP dvpavilon dv6000 with windows vista. I tried to downgrade to XP sp2. used the CD started installion, deleted existing partitions, made 2 new partitions FORMATED first partion C:/ completed installation. After system reboot by the installation procidure windows vista started as it it was with the same 2 partition as they were for vista same sizes, same users IDS. Repeated XP installation all the way from partationing. But in vain. The third time Hard disk was not available at all for installion For windows XP SP2. Long story, used KILLDISK program to make hard disk visible to the [OPERATING system]. latter decided to install Windows 7 and succeeded. i doubt my Hard disk while working with KILLDISK showed 235,000,000,000 (there were not zeros but some degits). finaly it gave me only 112 GB. WHAT VENT WRONG, WHERE THE OTHER HALF PARTITION GONE ????.