built-in sound and TV tuner questions

OK, so if I build my HTPC, is it possible to use the tuner from my plasma for recording? or MUST I get a tuner card right away?

Also, is it is fine idea to send the sound digitally (coax, toslink ,etc) from the mobo's built-in sound chip, or is it still advisable to use a separate sound card? I'l be sending the sound digitally to a receiver which will be doing the DAC job, so I don't see at this point any real reason to buy a separate sound card (or should I?).

You will need a tuner for your PC if you want to watch/record TV from the PC...otherwise there is no need for the HTPC to begin with.

Onboard sound is fine. If going over SPDIF, it's simple digital passthrough so having an add-on sound card won't bring anything additional to the table.