You can edit HD with FCP 6. Final Cut Pro HD was version 4.5 (I think, maybe it was 4) but after that they dropped HD from the name. If you are editing DVCPRO HD or HDV, you're fine. If you plan to be editing tape based formats like HDCAM, you'll need a capture card. AJA makes nice ones.
North Hollywood, CA
"We are the facilitators of our own creative evolution." - Bill Hicks