I think that your CPU will probably limit your graphics card's capability, but not to an extreme extent.
There is some kind of relationship between CPU/Gfx which is not obvious to most people, but I have seen this occurance several times.
For example a GF2MX scores around 1000 3dmarks with a P2 400Mhz, yet with a Duron 1Ghz scores over 2500 3dmarks. A Geforce 3 Ti200 is limited to about 4500 3dmarks on an Athlon 700Mhz Chip, yet increases immensely when placed in a 2.0Ghz system.
Cards such as the GF3/GF4/R8500/R9000/R9700 do not make heavy demands on the CPU, but I expect that the games you are likely to want to play using that card probably will. Cards which emulate DX8 features using Software (GF2MX/GF2Series/GF4MX/R7500/etc.) benefit a lot by changing the processor in Dx8 applications/games. In theory a GF2MX in a very fast P4/Athlon system could probably beat a Hardware DX8 card at the Vertex Shader test in 3DMark, as that seems to depend mainly on your CPU speed. However Pixel Shaders cannot be emulated through software and so must use relatively little CPU time.
Also, what memory do you have PC133 SDRAM or 200Mhz/266Mhz DDR, as the GFX/RAM transfer speed may be more of an issue with the R9700 than CPU speed ...