How can I choose a decent A/V capture card?

[Sonora 54]

I am trying to transfer some old Batamax & VHS tapes to DVD. For this pourpose I bought a Pinnacle Movie Box USB. This card is giving me troubles since day one. First, Studio 9 could not handle large videos and crashed every time as I was editing or burnng. So I decided to switch to Sony Vegas 6 and my results where excelent. Now I can't capture a steady image. I have a fearly good source captured in to a DVD and trying to re-capture in my computer for editing pourposes, and what I get is a jumpy-flickering and unstable video image. I have tryid several sample rates from 6000 Kbits/s to 2400 Kbits/s and the problem seems to decrease in lower sample rates. But I still get the bad image, particualry at the middle of the video (like if it is 50 min. long, trouble appears at minute 20, and from there on). I contact Pinnacle in Mexico (my home country) and they tell me that the problem es my processor Athlon 3500+ 939 with 1 Gb DDR memory. Can this be possible?

And my second question. Does someone know of any capture card that will work properly with my computer's configuration?

Thank you for reading this and would appreciate any suggestions