Security applies to all sections of IT.
You can have application security, network security and so on. each one specialising in it's own field.

Have a think, we have nothing better to do than...

They're both Server-Side languages, either will do. I just prefer PHP because it's open source :)

Yeh, you're probably better keeping everything at the server side.

Yes. you're looking to grab and STORE the IP Address of the client that's viewing the website.
This can be found at $_SERVER['REMOTE_ADDR'] in the PHP language.

You're looking to have some kind...

Yes setting up dyndns is a good solution.
Even better, you can use www.no-ip.com.
This comes with an 'auto update tool'
Which will update your IP to the domain name you've bought.

Thus, you can...

I recommend formatting your hard drive and installing XP SP2 from fresh.

If you're on a machine with SP1 and you're getting numerous infections, good chances are you're not going to get rid of...