What configuration of PC for local playing and transcoding

[xj]

Hello,
I am planing to buy new pc for my VLC Station, but I am not sure what configuration I should buy and the stability is important to me.

I would like to play DIVIX and transode it into Theora and this source send to a user.

I am also absolutly confused about the choice of Videocard, beacause I would like to run it on Linux but also on Windows (test new features of nightly builds).

At this moment I am absolutly satisfied with the ATI so called "Theatre mode", that allows me to play only video on my TV, but I do not know if Linux can handle it.

Could anybody explain me the differences between Video\Output modules (in VLC 0.8.2-svn-20050414) or give me some link pls?

Summary:
1. what pc configuration fits best
2. what videocard is best for both OSs (and linux mini how to)
3. the Output modules explaination

Thank you, thank you very much

Jan