Really? Exactly how old systems are we talking here? BlitzMax ran at an excellent framerate on both the TabletPC (WinXP Tablet Edition), my old desktop PC (GeForce III, Windows 2000) and my new desktop PC (Intel on-board graphics and Radeon X600XT, WinXP Pro) using nothing but whatever drivers shiped either with XP or the graphics cards in question.
I know a guy who sells casual games written in OpenGL and he has a 50% failure rate from Windows based customers. They just don't have proper drivers installed.
His failure rate on Mac is something like 5%.