WEI does not test your power supply. if you dont trust the results from WEI, i guess you should go with your instincts, or try something like pcpitstop. it will benchmark your hardware and let you compare it to other users test results.
Ah ahh. On about your HDD and from your specs you have the same drive i used to have (Seagate 160Gb) which is probably scoring 5.7 in WEI. Right? This is because it is a lower hardware version with lower cache etc.
I went up to a 500Gb Seagate HDD which now gives me 5.9 in WEI and i have noticed a considerable perfomance boost just from that in loading times and such.
On to your original question about a bottleneck. I wouldn't be surprised if your 2.4Ghz CPU may cause a slight one in some of today's games and even more so in future one's. Even on my C2D E6400 @ 2.8GHz running with my GTX260 i notice that my CPU is holding me back slightly.
All that i am saying is don't expect to see a major improvement. Has long as you keep that in mind you'll be happy with your upgrade and you should see "some" improvement at least :)
Edit: OH! and your next upgrade i would say go for the PSU, and try and get something branded like Corsair etc. Good luck with it all anyway
The graphics card will give you a good performance boost.
Depending on what you do with your computer, your 4GB RAM should be enough, unless you're doing graphics work.
The PSU possibly, depending on it's age and rating.
As your WEI pointed out, the next bottleneck you're having is the HDD.
You can try a better HDD or, depending on your budget get a SSD.
You will see a noticable performance increase, everything will be faster.
AS far as the RAM, if you currently have decent DDR2, I doubt you will see much of an improvement going to 1066 in real world use.
It really isn't that much difference, other than in benchmarks.
However, if you plan on Overclocking your Intel CPU, then 1066 RAM would be ideal.
As you can set the RAM at DDR2 800 speeds, and start Overclocking the processor. this gives more headroom for a stable Overclock as RAM speed will increase with the FSB speed.
At this point, faster RAM Speed in combination with faster FSB speeds will make a bit of a difference.
If you do not plan on Overclocking, DDR2 800 is ideal.
My 2 cents for whats worth.
And I completely agree with Dave. A SSD will give a huge overall system performance boost.
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