Is there a way to find my windows index score on xp?

None I've ever heard of, in any case it would be meaningless, the goal post will keep changing as new hardware and OS are available.
It's mainly there as a guide to indicate what you could improve to get a better performance, such as a better video card for gaming, faster hdd for quicker startup and so on.
Originally the top possible score was 6.9, I believe it's now aound 9, so you can see if you had say a 6.7 before which would have been a great score, you would now be chasing the new one.
I don't think you need anyone to tell you if you know, that you have a good system.
Those figures have been known to be rigged, so I wouldn't take too much notice of them.
I have an E6600 2.4GHz it does what I want, even if it is 2 and a half years old, my video card limiting it to 4.7.