Lots of versions of the optiplex--from big to tiny. Also the less than 300w power supply is too small. You have to measure the space available and look at the power requirements of any card you want to add. The Optiplex is a business model and not suitable for upgrading to a gaming computer.
That card requires a big power supply --
450 Watt or greater power supply with 75 Watt 6-pin PCI Express® power connector recommended (550 Watt and two 6-pin connectors for ATI CrossFireX™ technology in dual mode
Any Card that is DUAL SLOT will not work. The Desktop Requires Low Profile Cards.
The 4850 does not fit in that category.
Specific LOW PROFILE 7750 cards will fit.
The absolute Best card is the Sapphire 11202-10-20G Low Profile 7750.
However the card uses 55W of power and the spec says 25W.
The 7750 Low Profile is fine for the Tower as it uses 1 Slot. Do not be fooled there is another card that is a 7750 but its not LOW Profile and Will not fit. The one that works in all models except the USFF says Fits MINI ITX on the box.
Thank you ever so much you have answered that in one go,I have searched everywhere for this and you have done it,do think this will work with the standard power supply?,cheers.
The 7750 speedstep posted should physically fit. Power should be fine as well.
I have been running the very similar radeon sapphire 4650 ddr2 512 low profile in an optiplex 745 desktop for a couple years without probelms. I think the size (about 7 inches long) and cooler width and power draw are substantially the same.
Edit: I just measured my optiplex 745 and looked at the motherboard. Assuming you have the same stock motherboard, you probably want to look for a low profile card that is a single slot cool and no longer than 7 inches on the printed circuit board portion. Otherwise, you might hit the components along the side of the expansion slot (there appears to be a couple of tall capacitors on the board), or will hit the cpu shround on the length.
By the way, that microcenter page indicates that the sapphire 7750 low profile is 5.1 inches wrong, I don't think that's right, I think it is more like 7 inches long. It should still fit, but 5.1 is pretty short for a 7750, I think.