My desktop is set up to be able to run pretty much any PC game in the last 25 years. I can dual boot with Vista Ultimate 64-bit and XP Pro 32-bit, and I have DosBox installed on both OS' so I can run anything DOS based.... and lets be honest there is some absolute gold from the DOS era.
My Old School PC collection
Baldur's Gate + expansion
Baldur's Gate II + expansion
Icewind Dale + expansion
Icewind Dale II + expansion
Neverwinter Knights + 2 expansions
Champions of Krynn
Death Knights of Krynn
Dark Queen of Krynn
Keys to Maramon
Diablo II
Warcraft
Warcraft II + expansion
Warcraft III + expansion
Starcraft + expansion
Rise of Nations Gold
Age of Empires + expansion
Age of Empires II + expansion
Blood Bowl
Caesar II
Caesar IV
Centurion
Cyber Empires
Dune 2
Grand Theft Auto
Hero Quest
Keys to Maramon
Kings of the Beach
Lemmings
Lemmings 2
Lakers vs Celtics
Michael Jordan in Flight
Mega-Lo-Mania
Master of Magic
Monopoly
Master of Orion
SimCity (DOS)
SimCity 2000
The Settlers 2 Gold
SimFarm
SimTower
Yoot's Tower
Steel Empires
Stunts
Transport Tycoon Deluxe
TV Sports Basketball
Where in the world is Carmen Sandiego?
Football Limited
Civilization I
Civilization II MP Gold + expansions
Civilization III + expansion
Civilization IV
Colonization (using FreeCol)
Dark Castle
Pool of Radience
Curse of the Azure Bonds
Secret of the Silver Blades
Pools of Darkness
Hillsfar