I'm a long time Premiere user who's making the transition to FCP. I mostly edit HDV with Cineform Aspect HD as an intermediate codec. What I need to know is if I can convert my HDV files to Prores in FCP on ingest and how editing performance with Prores will be on a 2,6Ghz Macbook Pro with 2Gb RAM?

You won't be able to convert on-the-fly to prores with the Macbook. According to Apple's specs, you need either the uber-mac pro, or a dedicated capture card.

That said, you should be able to *EDIT* ProRes without a problem. I do it without a major problem, running the files off a FW800 external.