help with eval problems...

If I had this information stored in a database field, <img src="<? echo $content_output["site_logo"]; ?>"> how could I assign it to a variable and output it? I've gone thru the info on eval() @ php.net, but it's not getting thru my skull very well. I keep getting errors I can't correct. Can anyone give me some pointers? Any good tutorials on eval for php out there? Thanks!