Is GDDR3 backwards compatible?

Ok I am trying to buy a new video card for an older computer that has an agp slot. I have no clue what GDDR its supports whether its GDDR1 GDDR2 or GDDR3. It is an IBM Netvista 8303-K12 model. So if I get a GDDR3 AGP card will it work if my computer only supports GDDR1?