A bottleneck is not an event that happens suddenly and is fixable. All it means is that any one of your parts is not quite as good as all the others. This will ALWAYS be the case. Every computer has a bottleneck to some degree, whether it's a crappy GPU or not enough RAM, but it also depends on what the computer is doing. Obviously, in Prime95 the CPU will be the bottleneck, and in gaming it depends on the game and the hardware but will probably fall on the GPU.
In your case, assuming you're talking about gaming, your GPU is probably what's holding you back.
Just remember that a bottleneck is not a "problem" in the normal sense, and you can't fix it. It's not like a virus infection or a bad driver. If any of your parts are below the level of any of the others, you have a bottleneck.
i've lost count of how many times i've said this, (well maybe twice) they will always be a bottle neck, you can use it to leapfrog though. Lets say that you start with:
cpu = bottleneck therefore gpu is underutilised therefore upgrade CPU
now cpu is underutilised gpu is fully utilised and is the bottleneck next upgrade gpu
cpu is now fully utilised and is the bottleneck therefore new gpu is under utilised
that cycle might take 5 years and encompass many generations of tech, skipping whole generations, ugradability becomes less important providing pci-e still exists in 3-4 years time.
Only do the upgrade once performance is too low, and you get to re-use a lot of stuff, and only buy a little at a time.
in your case the GTS250 is the weakest link, whats your budget, whats your resolution?