one thing ... DDR is NOT SDRam ... that's the whole point ... dual data rate vs Single Data Rate (SD DD .. heh)
if you have SD, then getting the new vid card won't help, in fact, I'd get a new mobo that does DDR
if it's DDR, the new video card would help more ... the faster memory clock on it would make more of a pipe for your DDR ram to dump textures, instead of holding them, waiting for your slower card ...
I've played games on "medocer" systems with AWSOME vid cards that played well, if not good ...
If you've got the money tho, I'd say do both

(also, since you havea P4 3.2, I'm assuming it's DDr, I have NOT seen a SDR mobo for P4 3.2's yet ... )