I wanted to answer my own question of a couple of pages back, and give everyone the benefit of my 'geek week'. I can now record and play non-5C content flawlessly from my Seattle Comcast 6200 firewire output. The instructions on this thread for installing the appropriate driver do work well.
If you are getting audio glitches or video dropped frames on playback, pull out your motherboard manual and find a PCI slot for your audio card that does not share with your graphics card or HDTV card. ACPI sharing under XP DOES NOT work adequately for sharing an IRQ under .TS playback conditions, and the only way to get the audio card 'unshared' is to try slots, then look in Device Manager to see what's sharing IRQs with what. I finally found a slot for my Delta 410 that was unshared, and that cleared up all my playback glitches. XP still shares the IRQ with a couple of USB ports, but unless you're making heavy use of them during playback, that doesn't seem to matter.
So now I have my computer set up for HDTV recording capability similar to a VCR: I use CapDVHS to capture the stream, because I like the ability to schedule recordings manually or weekly. Leave it running and it does the job. The 6200 can be set to tune a particular channel at a particular time, so as long as the box is on, you're golden for recording.
For playback, I use Theater Tek 2.0. Yeah, it's a commercial product, and you have to pay for it. It's also widely considered to be the best software for playing DVDs. The new version has the unexpected (by me) ability to play .TS files. Set CapDVHS to generate files with that extension, set HD video to Overlay (not VMR) in TT, and playback is click and watch. No futzing with the captured stream is required, and you can use TT's chapter advance button to switch between programs in a multiplexed stream. How slick is that?
For reference, my HTPC is a medium-powered one- ASUS A7V333 motherboard, Athlon XP 2000+, 512k DRAM, Radeon 9600 Atlantis, Delta 410 S/PDIF out to my receiver. 480Gb of onboard hard disk, including 320Gb RAID 0 array. I did a recent 'nuke and pave' with a slipstreamed XP SP2 CD.
Last night I was watching a program previously recorded with Beyond TV 3.5 while CapDVHS was recording ER in the background. Didn't come close to maxing the system, and all was glitch-free. I'm becoming a pretty happy HTPCer- finally!