A few things
1. You can install XP Pro without XP Home, the XP Pro CD just needs to be bootable, I have installed XP Pro bunches of times without installing XP Home
2. Are you sure you even need Pro? Unless you plan to use it as a Remote Desktop host/server, connect it to a domain based network, or really overhaul the system, you don't need to use XP Pro, XP Home will suit your needs fine
3. Vista does have it's bugs and incompatibility, but you may just want to spend some time messing around with it first before completely erasing if from your hard drive, with no way of getting it back, who knows, it may work fine for what you want to do, then if it it becomes too overbearing, you can replace it with XP, or you can choose to multiboot later on
To install XP Pro (though Home may be more suited for you), put in the XP Pro CD and reboot the computer, as the computer boots look at the splashscreen, it should say something like "F1:Setup" or something like that, whatever that says tap that key on the keyboard to enter your BIOS, the most common BIOS entry keys are F1, ESC, the ESC on the number pad, and Ctrl, go to where the boot order list is and select the CD/DVD drive (whatever the main optical drive is) and set that to boot first, followed after the hard drive, then save your settings and exit out of the BIOS, after the computer reboots, wait for the message saying (Press any key to boot from CD...), then press a key on the keyboard, the screen should turn blue and say "Windows Setup" in the upper left, on the bottom of the screen, there should be a gray bar, that should show all the files it is loading into the RAM for install, continue as normal until you see the hard drive/partition selection screen, remove all partitions so it shows up as 1 blank hard drive (unformatted), then select the hard drive and begin install, do a full format with NTFS, it will then format, install Windows then reboot for setup, when you reboot, when the message comes up asking you to press any key to boot from CD, don't do anything, it will skip booting from the CD and boot from the hard drive, and you will go through the second half of installing and setup, this is where you put in your time and date, your system language, usernames, internet connection, and all the other setup information, then it will reboot again, this time running Windows as normal, then you can log in and use Windows, at this point, it is going to bug you to activate Windows, if you are connected to the internet, it will just send the information to Microsoft and you are done