To elaborate on Schadenfroh's reply, paying more for 256MB on a card as slow as a 9600 is a joke. At that performance level, any extra money you have is better spent on a faster card that will be enjoyed all the time, not on more memory that will be enjoyed once in a blue moon.
The 128MB Pro is 400/600MHz. The 256MB card is 400/660, so it should be faster (if the specs are correct, as higher speed memory on a 256MB card is unusual, so this may be a typo). The
$159 9600XT is 500/650, and should be even faster.
If you have a 300W PSU, though, you'd be better off with this
$159 9700. If you want to run dual CRTs off the video card, consider paying the
extra $10 for the retail version, as it includes a DVI-VGA adapter (and an S-video cable). If every $ counts and you don't need the S-video or composite cables, get the OEM version and add a DVI-VGA converter for $7. You can see on Allstarshop's pages for both cards that the 9700 is superior to both the 9600P and XT with AA+AF, mainly because of its far greater memory bandwidth (256-bit 540MHz vs. 128-bit 600-650MHz).
If you can spend more, NewEgg sells a Powercolor 9700 Pro for $183.