I have a HiPix connected to my Toshiba TW40X80. I'll try to answer the questions I understand.
It's easy to connect to my YPbPr inputs using an Audio Authority 9A60 transcoder.
HiPix (as do all Janus-based cards I'm aware of) has an analog switch at the output. So, if you use the included "pass-through" cable from your VGA card into the HiPix's port, you can simply use the UI's "Full Screen" radio button to select either VGA display or HiPix's video for your RPTV. Note that if you select the analog pass-through of your VGA display, the display format must be compatible with the requirements for your RPTV; the HiPix doesn't do any scan conversion. For my Toshiba TW40X80, I've only successfully used VGA at 640x480 (HDTV is at 1920x1080i), but I haven't tried PowerStrip yet.
If your RPTV has VGA in, it is compatible with the HiPix directly. If your RPTV accepts RGB, you'll need a VGA-to-RGBHV breakout cable. The sync also is carried at least on the G, so if your set doesn't have the H and V inputs, I don't think you need to worry, but I haven't tried this myself.
Note that the HiPix can transcode RGB into YPbPr without the AA 9A60. However, if you choose to use the on-board transcoder, be aware that the VGA analog pass-through is not transcoded. This means that you'll need to watch your VGA card's display on a separate monitor, and you won't be using the pass-through cable.
I can't comment on HiPix's overscan vs. other HD receivers. But knowing how a transcoder works, I don't see how there could possibly be a difference between RGB and YPrPb signals.
Some people are now excited about the AccessDTV card. It is now shipping from Digital Connection. There are threads about that card's benefits and drawback that you may want to read before making a purchase decision.
Hope this helps,
[This message has been edited by yogaman (edited 03-30-2001).]