The only thing I can say is that the problems are not XP-specific. I've been running the Windows 7 Beta (and later, the Release Candidate) in dual-boot form for the last few months, and the same capture issues show up there.
One additional thing i've noticed, though, is how my M-Audio sound card (Delta 1010LT) now adds a fair amount of static to recordings. It was somewhat an issue before, but it's become much worse, to the point of me having to resort to recording audio via my DVX-100 over firewire (as a DV signal). From reading around online, other people having this issue are saying it's an IRQ conflict. That makes some sense given the amount of stuff I've crammed into this computer, but it's really dissapointing given that if I have the room to add two expansion cards, I would figure that would mean I could actually use them without them tripping and stumbling over each other's toes.
I really hate to say it, but at this point, I'm ready for a Mac (or Macbook) Pro. Having recently done some basic editing using Final Cut Pro on a friend's Macbook Pro, and having them not having to save their project for a day and a half before worrying about crashing, I think it's safe to say they've worked out some stability issues. Oh, and that's editing using 2K footage.
Also, Apple Prores is quite possibly the coolest editing codec I've ever worked with. If they ported it over to PC as a codec Premiere Pro could capture to, I would probably use it for everything.