I have tons of old games for a variety of systems that I never got around to playing. In search of something I could play while waiting for data builds at work, I reached in to my pile of old games and pulled out Ascendancy, an epic space strategy game circa 1995. Unfortunately, my laptop isn't capable of playing it. Why?
Ascendancy runs in MS-DOS, not Windows XP.
Luckily, someone at work pointed me to an open source app called DOSBox. DOSBox is a full DOS system emulator that effectively creates a virtual 486 on your desktop. Do the terms Tseng ET4000, Gravis UltraSound, and EMS sound familiar? They're all emulated in DOSBox. Ascendancy and other classic DOS games I've tried are fully playable.
Although the official 0.63 release of DOSBox works fine, there are several updates and bug fixes in CVS that make downloading an unofficial CVS build worthwhile. (Get it here: http://ykhwong.x-y.net/page.htm) In particular, the CVS version of DOSBox supports DirectX PixelShaders for some very nice graphics scaling.
Time to dig more of those DOS classics out of the closet and get gaming!