You can capture DVCPRO into Vegas over firewire no problem. I’ve done it before, its all DV all the way.(natively)
You mentioned an sdx-900 that camera can also shoot in DVCPRO50 codec, that’s where you would need to download a codec to edit in Vegas. http://www.mainconcept.com/codecs.shtml#dvcpro
FCP can capture DVCPRO50 via firewire. You would need to transfer to hard drive the footage to edit in Vegas. If you have a Mac around with FCP capture there – then transfer it over to Vegas, then back to the Mac for PPT. Or get a DVCPRO50 deck that has SDI I/O and capture it over SDI.
If you're shooting on the SDX900, presumably you're wanting to use the highest-quality DVCPRO50 mode, right?
If so, the answer to your question is: yes you can edit it natively in Vegas (if you get the codec), but no, you can't capture the footage.
Probably what you would need to do is get a deck and capture the footage on an FCP system to an external hard disk, and then you could use Vegas to edit the footage off that hard disk.
I posted the link to the free Matrox DVCPRO50 codec that works within Vegas -- search the forums here and it should show up.
Doesn't Final Cut capture in Quicktime format?
In my experience, Quicktime DV captured on FInal Cut performs extremely poorly in Vegas. I suppose you can get around it via Gearshift? (seems a little silly, but I suppose it'd work)
Quicktime to AVI conversion: Do any programs convert the video data without recompression? (I don't know of any.)