depends on your resolution at 1280x1024 u will just get by on video memory, yes you cpu will botle neck it any cpu will unless its something like one of the new q6600 chips or the e8400. but it wotn be much you should score near 10k in 3dmark 06.
At that resolution then yes your rig would be bottlenecked by your CPU.
but that doesn't mean you won't see good performance...it just means that your CPU is the weakest thing in your link and you'd see a large difference with an upgrade.
look at it this way. I have an AMD 64bit 3200+ 2ghz and an 8800GT 512mb. I cannont play crysis on high cuz of the cpu. upgrading my x1600 pro to an 8800gt only gained me about 20fps. when my new e8400 dual core 3ghz gets here, that will be about a 30-40fps gain. (i think)