|"my laptop came with vista already installed and ready to go, so I don't have an installation disk for Vista"|
Manufacturers rarely supply disks anymore. Instead, they place the installation files on a hidden partition on the HDD so that the user can create the disks. Most people don't bother (or don't even know they have the option). Try looking at the Start > All Programs menu, the disc creator software is probably still there unless you deleted it.
"I've hated Vista since I got it"
So you've been struggling with Vista for what, 5 yrs or more & have finally decided to replace it with an OS that's over 10 yrs old, nearing it's end-of-life & rapidly losing support? OK.
You didn't post the make/model of your laptop so it's impossible to provide clear instructions on what to do. Unless it's a higher end model, it's probably not very game worthy, regardless of the OS. And I'm guessing it has a SATA HDD so that means you're going to have to jump thru some hoops to get XP to install. Here's a how-to that explains it:
And as phil22 stated, you may have a problem finding drivers so before doing anything else, see if you can track down XP compatible drivers for the motherboard chipset, graphics, sound, network, wireless, etc.