USAFRet :
Craig M :
spooky2th :
There are drivers for windows XP 64-bit and 32-bit at the MB web site, so you should be able install XP.
MB drivers and tools
http://www.asus.com/us/Motherboards/A88XMA/HelpDesk_Download/
Can I download a windows 7 trial version or something for the time being?
There is no Win 7 trial. You can buy one, and delay activation for 30 days.
You might try the current Windows 10 Tech Preview
W10 Tech Preview is working quite well for most people (it's been updated a few times). As a recent OS it comes bundled with drivers so I doubt you need any for your motherboard.
There may be some drivers you would use the W8 64-bit version instead. For VIDEO you'd likely want the Windows 10 version. There will be a BASIC version installed but you'd want to find the official W10 version from AMD (or NVidia if that's the case).
You can use a USB method.
http://windows.microsoft.com/en-ca/windows/preview-iso
and
http://www.extremetech.com/extreme/191295-how-to-download-and-install-the-windows-10-technical-preview
I don't recommend buying W7 or W8 since you'd likely want W10 in the end. The preview is good until at least 30 days after the Summer (August?) release likely and if you BUY it that can be done digitally and the preview will update itself so you will NOT HAVE TO REINSTALL it.
You would have to BUY it, however there's been no word on pricing. Microsoft's pushing it as a free upgrade to W7/W8 so it's possible they'll offer it new for a discount for a short time over what you'd normally pay but that's only a guess.
Other:
I'm a little baffled why you'd want XP in the first place. If you own a legal install disc I still wouldn't recommend it; as well, if it's already been installed to a computer you can't reuse it likely (there were transferable versions which cost a lot more.)