Included with your 4850 should be an adaptor. My 4850 has 2 DVI ports. It also included an adaptor that does DVI--->HDMI, and another adaptor that converts DVI---->VGA. If you bought your 4850 used you might not have gotten all of the included adaptors and most likely will need to order one off of ebay.
You said you have a port that looks like an HDMI port. If thats the case and your monitor has a DVI port just get an HDMI--->DVI cable.