Server Advice

So I decided to 'convert' my desktop into a server computer for my house. It'll store all of our video and music files as well as host servers for our gaming needs.

I've got a few questions for those of you who have done something similar to this or are more knowledgeable than myself.

First of all, it's an AMD XP 2200 with a Radeon 9700 Pro and 512MB of Corsair XMS PC3200 running XP Pro.

1. I have access to a free legit version of Microsoft Server 2003. Should I run Server'03 instead of XP Pro? Pros and cons?

2. I want to buy a TV tuner so that I can run my cable through the PC with coax then to the TV with S-video. What features should I look for? Are any brands particularly awesome? Links?

3. I'll probably end up buying some more RAM and possibly another HDD for it. I don't think there's any need for a better video card (even down the road) if I'm just going to be hosting with it. Is that correct?

Thanks in advance.