Where to get older bootcamp drivers?

This website contains download links for the latest version of the Boot Camp WindowsSupport for older devices:

For Windows XP, Apple has provided Boot Camp Drivers Update v2.1 and v2.2 which…

is intended only for use with Microsoft Windows XP and Microsoft Windows Vista running on a Mac computer using Boot Camp.

Both updates require Boot Camp 2.1. It also notes that…

This download contains complete copies of Boot Camp Windows XP Drivers (version 2.1). If you have Boot Camp drivers already installed, it will update them. If you do not have any Boot Camp drivers installed, it will install version 2.1 drivers onto your already installed Windows OS.

This should fix your XP issue, since it contains the latest XP-compatible drivers. If not, your only option will probably be Windows 8 (or Windows 7).

With regard to installing Windows 8, Boot Camp 5 brings full Windows 8 support.