As said above, I've been asking for help to write a FAQ up for a Guide that I'll hopefully be getting out sometime this summer, and it can be found here: http://www.sythe.org/showthread.php?t=630573
There are addons that you can use to help you level, and make your WoW Experience much more enhanced. A list of great addons can be found here: http://www.sythe.org/showthread.php?t=631841
In my opinion, you should pick which class that you think sound cool, and would generally be fun for you to play.
Paladin - Can Tank / Heal / DPS - Great in PvP
Rogue - Massive DPS if you know your Spec. Very fun and easy to play, with many benefits.
Mage - Great at kiteing, and can be the highest DPS in Raids a lot of times.
Druid - Can shapeshift into many different forms. Can Tank / Heal / DPS
Priest - Can heal or go Shadow Spec for DPS. Great to play if you like healing.
Death Knight - Must have a character at level 55 and have WoTLK to play. I don't like 'em.
If you have any additional questions about starting the game, send me a Private Message, and I'll be sure to get back to you.
If i was you i would choose a easy beggining class and you should pair up with someone using that gain more exp thing and get someone from your guild to just run you and your mate that you are doing more exp with through instances a very fast way to get to lvl 60 got my alt to lvl 60 in 3 days.
You should really map out what you are planning to do before you start. It really sucks when you get halfway to 80 and you think to yourself, shit I should of been ______.