If you're using 4xAA at 1024x768, yes you'll notice the difference, but it won't be mind-blowing.
However, the X800 will let you play at a higher resolution with 4xAA and still get a great framerate. So if that's a high priority to you, and you have wads of cash lying around, you could do worse I guess.
Me, I don't think I'd bother just yet.
<b>Radeon <font color=red>9700 PRO</b></font color=red> <i>(o/c 332/345)</i>
<b>AthlonXP <font color=red>3200+</b></font color=red> <i>(Barton 2500+ o/c 400 FSB)</i>
<b>3dMark03: <font color=red>5,354</b>