Take Terry's advice seriously. Booting multiple OSes on a system can be a complicated thing to set up if you don't understand the procedure.
Read the guide and follow the instructions below to get XP working.
Assuming you've restored the system using the recovery partition:
1) You'll need to shrink Vista's partition (Usually labeled "OS" and is drive C:.) to make room for XP. You can do this in Disk Management by right-clicking on the Vista parition and selecting the shrink option. If you are unsure about the amount of space to take away from Vista's parition, use the default. Vista well automatically, by using the default, shrink half the partition. So if you had a 100GB parition for example, your Vista partition would then be about 50GB after shrinking it and you would be left with 50GB of free space in which to use for XP's partition. Now, i'm assuming at the moment you have only Vista on the system since you've used your recovery partition to return the computer to the factory default state.
2) Create a new parition from the free space taken from the Vista partition in order to hold the new XP installation. I'd go ahead and do a quick format in NTFS and give it a volume label like "XP" or something that well help you to remember which parition you need to install XP on later.
3) Boot the computer from XP's cd and when the partition screen comes up, highlight the newly created partition and hit enter to install XP there.
4) When XP is finished installing, Vista well still be on the system, but when you boot the system, it boots straight away into XP. Follow option 1 from my previous post to get Vista working again and add the entry to dual-boot with XP.
Do yourself a favor and use HnS. You never know when you're going to need Vista's restore points in case there are problems. XP is a restore nightmare for Vista's restore points.