Q: Powerbook G4 as HTPC to 4:3 CRT TV / app and box recommendation?

Hi--

My first post here.  I've done quite a bit of research here and elsewhere, and I still can't figure out the best solution for my particular setup.

I'm getting a new MacBook Pro very soon, and my 1.5 Ghz Powerbook G4 is still alive and (sort of) kicking.  I intend to use the PB for a HTPC/media server, with the media coming from a LaCie 7200 RPM FW drive. 

The monitor is a late 90s, 4:3 Sony CRT TV that I like (I'm not ready for HDTV upgrade). 

For sound I plan to use an old MBox 1 as my D/A converter out of the PB into my 70s Pioneer stereo amp/receiver; I'm not terribly interested in 5.1 etc at this point.

My questions are:

What app/software do you recommend for organizing/navigating the media?  XBMC, Plex, etc?

How should I go about connecting my PB to my 4:3 TV so that wider-than-1.33 aspect ratios show up properly letterboxed on my TV?  I should note that my TV only has composite and S-video inputs.  I tried just hooking it straight up from the S-video output on the PB using the S-video- to - composite adapter (I didn't have an S-video cable handy to try that direct connection), and it looked awful no matter how I set the resolution.

If there's no way to connect the PB to the CRT directly with decent picture quality and correct fomatting, what box would you recommend to help make the conversion?  Or is a box just a good idea in general?  I do have a first-generation Roku, which does not have the USB jack.  I'd also prefer a wired connection of some sort.

Is there anything else I should be looking at within the confines of my setup?

Sorry if this is a bit long-winded, just trying to give all pertinent info... 

Thanks for any guidance, and I'm sorry if this has been covered elsewhere.