I was very excited to have a new computer and OS until I tried playing older games on Windows 7. After a month of headaches, I set up my computer to dual boot with Windows XP. Any game that was released pre-Windows 7 just gets installed on the XP side of things.
It's a bit terrifying to do if you're not used to it -- just back up your data. The worst that happens is you have to reinstall your operating system and data.
The next operating system is likely going to be less friendly to XP-era games, so it might soon be a necessity.
As far as obtaining a copy of XP, all you need is the license code -- often found on stickers attached to old PCs and laptops. XP is supported through 2014.
Here's a guide to installing an XP/7 system.