How long does it take to download the blockchain? It's been over a day and still going I'm a newbie to bitcoins, and need some help!

I downloaded the Bitcoin client and installed it on my laptop.

It is 'Synchronizing with the network' and has been doing this for over a day. Is this normal? I have broadband internet and sometimes download large files in a resonable amout of time so I'm pretty sure its not my internet connection speed.

I understand it is downloading the blockchain thing bit by bit but does it really take this long? Will I have to do the same if I were to change laptops or get a new computer?

Also, whilst it is 'Synchronizing with the network' it totally slows down my laptop, so much so that it takes ages to even launch my internet browser. Is this normal? Will it always do this when I run the Bitcoin client, i.e. slow the whole system down, or is this only the case when it is 'Synchronizing with the network'?

Many thanks!!
You probably don't want to download the blockchain

The blockchain currently weighs in at about 144 GB (check current size) 
Assuming you have solid 2 megabytes per second download speed, it would take around 20 hours just to download them. 
In practice, this takes much longer, as your computer will verify every block individually, which takes some time.

Also, if you're not doing any mining, it may be wise to look into a lightweight client such as MultiBit or Electrum.