Sure enough. I got a 12' S-video cable from Best Buy (about $25), and life is good. I just plugged it into the TV and the PB, tinkered with "displays" for a second, and - presto - it works. Thanks for the help, guys. Everything seems to work fine..and I appreciate the advice.
The one snag I've had is that when I don't disconnect the TV (display), occasionally my mouse will go wandering off into the blank TV screen, which always leaves me puzzled as to where the hell my cursor went (especially when the screen is off), but that's easily remedied by just disconnecting the display again.
Anyway, thanks again. If anyone else needs advice on this, I'm happy to share my tiny success story in greater detail.