if you were editing AVCHD, I would say:
PS primarily uses the CPU to render -- and Intel CPUs perform better than AMD. The i7 is best for video, but many people can edit with i5s for projects that aren't too complex.
There is a diminishing return for getting a video card much beyond a certain baseline card (a GTX 650 for example) -- since PS does not leverage the GPU except for some EFX.
And the built in graphics power available from a current model Intel system is sufficient for the majority of projects....
But since you're editing tape -- a much less demanding medium -- I think your system (CPU & GPU) ought be powerful enough.
There are likely PS things that colour, Hunt, JJN can help you work through, that can improve your PS performance and speed its rendering. (I would tell you how to clear the cache, but I'm not at my editing PC).
BTW-- you mentioned that you run XP -- what are your plans for updating your OS ??
The simplest, least expensive fix might be to save all projects, do a clean OS upgrade to Win 7 or 8 -- and then reinstall PS14.
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