It may not always be possible to replace Vista with XP on newer systems, simply because there aren't always XP drivers.
Before you even attempt this, you should always check to make sure there are drivers available for your hardware. This is especially true for laptops.
Also, if you do a search on Google or these forums, for that error message you're getting, you'll see it has been answered numerous times already.
How to downgrade from Window Vista Basic to XP professional SP1?
I tried to format Vista and then install XP but when i am installing XP, computer show "could not see your Hard disk"