Where Can I learn the commands at?
You should absolutely start with the gentoo handbook from page 1. It will tell you exactly what you need to do (including the commands).
As for what cd to download - you have a Pentium 4 processor which is an i686 (download x86). So you can chose between the minimal install cd and the livecd. I would definitely go for the minimal cd and follow the handbook. This way you will learn the basics of a linux system and will be more aware of what is happening to your computer.
World of Warcraft can certainly be played on your computer. I have a P4 with 1Gb DDR and GeForce 5500 and I play WoW at an FPS of 16 (a bit choppy, but that's due to my gfx-card). You will need either cedega (I use that) which can be downloaded at transgaming.com for about 5 euro/month or use a program called wine to set it up (ask around for this).
Some other Windows programs can also be installed by wine. But, luckily, there is no reason to do this as 99% of all windows programs have linux counterparts (as the previous post pointed out). Words is replaced by openoffice.org, photoshop by gimp, aim by gaim, windows media player by amarok, rhythmbox... the list is long.
However, don't haste - you have lots of things to do (install base system, X, alsa, gnome/KDE/Fluxbox, nvidia-drivers, etc, etc) before you will be able to play WoW. So, start at the handbook for x86, page 1.
