Can i squeeze a Radeon HD 5850 video card in a dell optiplex 755 minni tower? I know the power plugs will need attention
First, you would need to upgrade the power supply. If you have the MT case (regular size Optiplex case like the ones in my office), then yes, a HD5850 will physically fit (you might have to move some wires/cables a bit. This case will also accept a standard size power supply, so you have options there as well. You don't have to use a Dell power supply with the MT case.
What is your budget for a PSU?