How to log in to ichat?

Hi im quite new to using macs, I have used them at college for the last two years, but have started to use them on a more regular basis now

(Please forgive me if this is one of the most stupidest questions ever)

How do i log into ichat, do i need to register for an AIM screen name?

What is a .mac account can i log on using one of them? Are they free?

will i be able to chat to my friends on msn using ichat or can i only chat to other ppl using ichat?

I am looking forward to using ichat especially full video chat this is something i was looking to do when i was a pc user but could never find anything, its so nice stuff like this is build into macs

Anyway thank you for any help (please dont be to harsh about me not knowing this stuff)

The following article helped me to configure iChat to work with MSN users. Give it a good read and I'm sure it'll work for you too.

You will be able to have a video chat with your MSN buddies but AFAIK there's no audio at this point in time.

Guide to iChat (and Adium)