Better Graphics Card vs. More Memory?

I just recently bought a Gateway Laptop with 4GB DDR2, but my graphics card is only 128MB. i would really like to have the OPTION of running higher end computer games but unfortunately, buying a larger Graphics Card is out of the question, so would it make a difference if i bought more RAM? or do i even need more ram in the first place? any info on the subject would be mucho appreciated :) thank you!