hell no.

you will need the other expansions for Cataclysm, I am sure, but you could always just get them as you hit 60, 70, and 80. 
 
EDIT: There is a bunch of content that cataclysm will give you, without you getting it even.

The game has been tweaked so much that you'll be through the main land very quickly. I would suggest not buying wow though, because it's poo.

If you buy vanilla WoW and Burning Crusade (the first expansion) together (in the WoW Battle Chest) you save $20, but if you're not sure about getting into the game, just buy vanilla WoW. 
 
And yes there's a free trial. You will have to download a LOT of huge patches so hopefully you have a fast internet connection.

Not likely. The only thing it will restrict you at the beggining is making either a Blood Elf or Draenei character, outside of that it's all later game content.

Get the free trial. If you want to continue playing, I'd get the Battle Chest. You get to make a Draenei or a Blood Elf, which have way more polished starting areas than the other ones.

you should play on the realm Burning Legion :)

Yeah, there's a free 10-day trial you can download. Just be careful.

I'd suggest buying them all at once, but I suppose you could just play the original WoW until 58. 
 
It would restrict some areas and talents and maybe some other things.

don't play world of warcraft. period.

" @PepsiPat:   And yes, you'll need the expansions for Cataclysm :) "

wait for the old republic and then decide  on an mmo.

Only if you get to 60 and want to advance....Or to play a blood elf because they're freakin' sweet.

You get all of the content from each of the expansions except for the raised level cap and access to the new zone without buying them. So as @TheMustacheHero: said, wait until you hit level 60 and then decide if you want to keep going. You won't gain anything from buying the expansions before you hit 60. Well, you could play as a draenei or a blood elf, but that's about it.

Thanks for the tips.

don't get addicted 
you'll die

" Yeah, there's a free 10-day trial you can download. Just be careful. "

Youll need the first expansion at level 60. You won't be able to enter Outland or level past 60 till you have it.
Personally, I'd wait till you need them. Its possible they may price drop them to get ready for Cataclysm.
 
I recently quit playing after playing since launch. Its a fun game if you can get into a guild with some fun people, its defiantly a better social experience then 'game'.

i'd get burning crusade at least because the blood elf/draenei starting areas beat the shit out of the regular ones, at least pre-cataclysm
 
once you're done with those you can probably level through instances or something and see as little of the old world as possible

To be honest i don't see why you wouldn't get Burning Crusade and Original WoW together. Each one is £10 and a game card would set you back another £20. £40 doesn't seem to unreasonable for a game which is as big as WoW, although admittedly it is several years old now. I'd steer clear of Lich King for when/if you reach the level cap. 
  
Of course this is talking solely from my English perspective.

WoW is very addicting, beware.