security issue

Hello all,
I have been visiting this forum for the past few weeks to get tips how I can set up my very first PVR. This is what I have in mind.

I going to use my old pc for this purpose. Atholon XP 1800 +, 512 MB RAM, 80 g storage, PVR-150+Sage (bundle) and a wireless card 802.11b.

I have satellite receiver from Dish Network and have SBC DSL service. Since my DSL/Router is far away so that's why I picked the wireless card for my futire pvr.

I am going to hide my pc behind my entertainment center

This is what I want to achieve.
1 . Be able to schedule and record programs using a remote control (I think the remote that comes with the bundle will work. If not then please tell me what can I do). I want to do all the scheduling using a remote control.

2. Want to watch all the AVI and DIVx or ripped DVDs on my tv. The way I want to do is to do all the ripping on my main pc in my office and then copying all of that to my pvr pc using the home network on wireless.

Here are my questions:

1. Is the setup I am planning is good? Are there any potential issues that I may have overlooked?

2. Is my pvr pc needs internet access to download tv guide on a regular basis? If yes then what about the securtity ? I mean this pvr pc is going to be used as a passive pc, will have nothing except media files and OS (Windows XP), so do I need to install any virus protection?

3. In case I install virus protection software, will they slowdown things? Also how you guys who already have pc based pvrs update your pc with latest security patches and other critical updates?

Thank you all in advance.