Well, first of all, PPro can’t tolerate large projects. I’ve had medium sized projects (15 hours of source video and some other stuff) and the projects take literally 20 minutes to load. So the first thing I would do is find a way to keep the video files separated into smaller projects – if possible. It will be worth the extra effort to keep it a bunch of small projects.
Secondly, obviously XDCAM will not play off of USB drive. I have SATAII drives that just managed them at draft quality.
Third – I don’t know about sharing the footage on two systems – you might be better off with some duplication. I have my systems set up with External SATA Hard Drive Docs. If I need to move the project, I can pop the drive and move it. The Media Preferences matter here – I target the files to the same drive but the database to the c: drive. When a project is moved, it has to build a new media cache database but not the audio files or index files – usually. I am on CS4 so the media preferences are likely different in CS3 – can’t remember anymore.
Otherwise, a fiberchannel network drive…???