My new graphics card doesn't work

I have a 20" iMac Aluminium MA877 with HD2600 PRO. Just today I update it with new ATI MXM II HD4650 1Gb from Acer (http://cgi.ebay.com/ATI-HD-4650-MXM-II-V......) card. Physically it fits very well, the PCB design is pretty much the same. But unfortunately after power on the Mac I've got the black screen.

Googling I found that may be I need the EFI update for this card.

Could someone help me to make it work?