Not to bore everybody to death with Mac content again, but just to get it on the record, here's a process for cross-platform capture, editing and viewing.
1. Capture in Windows with the included ArcSoft package.
2. Import the resulting file into EyeTV 3.x using this procedure:http://forums.elgato.com/viewtopic.php?p=14609#p14609
3. Edit in EyeTV. The resulting file will be in a "Live Recording.eyetv" container in your Home>Documents>EyeTV Archive folder. Change the suffix to .ts (or really to anything) and you can open it as a folder. The edited file inside will be a long string of numbers followed by .mpg. Rename it as you see fit, leaving .mpg as a suffix. Quicktime will not play this file.
4. Put the file in a directory accessible by Plex, then open Plex, and navigate to the file normally. It should play back fine.
This is a pretty tedious process, requiring two real-time recordings and use of a bleeding-edge-new playback app (Plex), but it does work, and the end file does not get reencoded at any point. You're still seeing the original video as recorded by the Hauppauge box.
ElGato has hinted that they may add HD PVR capability to EyeTV down the line (I'm signed on as a tester in case it ever sees the light of day), which would presumably provide a soup-to-nuts Mac solution, but for now that's still vapor. So don't trash that XP partition anytime soon...