Yes, when you say your computer is DDR2 I'm assuming you mean the system RAM is DDR2, System RAM and VRAM (video random access memory) are not at all linked and have no bearing on eachother in terms on compatibility.
the video card is not dependant on the type of system ram you have. look at the system requirements for the graphics card, its amazing how many people fail to read these things. Its like asking "what fuel goes in my car?" instead of reading the god damn label on the fuel cap or manual. Or asking someone "what day is it?" when you have a calendar right in front of you.