Your hardware should be more than adequate. I tried various capture programs, and the one that gave me the most consistent results was the Mainconcept capture (it comes with the encoder program.) You should try capturing at 720x480 whenever possible. You might want to turn off cropping and see if that helps (it could be taking up extra processing cycles, and you can always crop later.) Also, what format are you saving to? MPEG? (bad) RGB? (eats up disk space) Have you tried HuffyUV?

You might also want to look for the latest drivers for your card. The official drivers for my card wouldn't capture at 720x480, but I found third-party drivers that would. I still don't understand this, since they are for the same videocard, but go figure.

Lastly, as to hard drives...how much space do you have left over, and when is the last time you fragmented the drive? A Huffy capture of ANH is 35-40 GBs, and an RGB capture can top 200GBs. You might want to consider getting a second drive and dedicating it to captures. Your 'puter will run faster if it's not capturing to the same drive your OS is on.

I hope something in all of this helps.

[EDIT] Just saw your site. You are using Huffy (good), and your pics look very nice. Good Job so far.