ATI Radeon HD 5770 Graphic card for Mac Pro 1.1

That is not a Mac card, so it may not show Boot Screens AT ALL, or only on wacky connectors such as a VGA display on the second DVI-I port.

It appears to have TWO Molex power connectors instead of the standard aux power connector, so using it as-is would mean disconnecting BOTH your Optical Drives and using an extension cable and making a spot to snake the wire (maybe cutting a hole in the sheet metal).

If it still has the standard aux power connector on the board, you could use ONE standard 6-pin aux cable instead. Those have three 12 Volt pins and three returns.

There are better choices:

User Tip: Mac Pro silver tower (2006-2012) Replacement Graphics cards

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A standard Mac 5770 is a good choice, but the card you linked is a PC card. I would NOT suggest a PC card if you are going to use SFOTT or similar hacks to get Mavericks or Yosemite on your Mac Pro 1,1.

The Mac version 5770 looks like either of these:

Note: Two slots tall, ONE DVI-I connector, TWO Mini DisplayPort, NO HDMI. All three ports can be used with the correct adapters, but more than two "Legacy" (non-DisplayPort family) requires at least one ACTIVE adapter, about US$30 additional for ordinary displays, more for wider than 1920 wide.

The PC tends to have captive aux power cords in the chassis. The Mac has connectors inside, not cables, so the Mac convention is the 6-pin aux power cord(s) come with the card. If you find a card without the cord(s), aux power cords are readily available in the US for about US$10 + shipping.

The underlined blue text is a link to an article on the subject:

User Tip: Mac Pro silver tower (2006-2012) Replacement Graphics cards

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Without hacking the OS, the 1.1 only goes to Lion. ML and later require a 64 bit EFI but the 1.1 only has a 32 bit EFI

http://retrocosm.net/2014/11/07/mac-pro-11-yosemite-install/

Did they cut off the 6-pin aux connector? if the standard 6-pin aux power connector is still in place, you can power it easily, but you will face these caveats:

If you are Meet ALL of these:

• running 10.8.3 or later AND

• don't care about "no boot screens" etc AND

• can re-wire or otherwise "work out" the power cabling, THEN:

You can use many more cards, even most "PC-only cards".

In my opinion, it will be awkward at best.

This is the power cable that ships on Graphics cards for the Mac Pro:

http://www.amazon.com/PCI-e-Power-Cable-nVidia-Video/dp/B002UR1654/ref=sr_1_3?s= pc&ie=UTF8&qid=1423247145&sr=1-3&keywords=6-pin+aux+power

If the connector on the card has been removed for those two white Hard-Drive Molex cables, you are facing a difficult battle inside your Mac Pro. I would return that card and find another.