What is the best way to get to madrid? how long is it by train?

check out europebyair.com
iberia.com
you can find some GREAT prices on flights, in some cases cheaper than a train ticket. I believe it is about 8 hours by train, but only about an hour by plane.
I have plane tickets for the same journey in July and paid about 38E.

There are fast trains called "TALGOS" that connect Barcellona to Madrid. They take about 6 1/2 hrs from Barcelona to Madrid.
for more info have a look at www.renfe.es or www.renfe.com
there is the english version too

I'd also investigate air option. There's an hourly shuttle between BCN and MAD, using dedicated terminals, so it's pretty hassle-free, and with fares war going on it can also be pretty cheap.

In addition to Iberia, check SpanAir (www.spanair.es). Book your flight on either airline ASAP to get the best price.

Hi SB1020, I think the Talgo train between B and M is a train hotel, Spanish train hotels are great. Lots of confort, some have Gran Clase which is not expensive for what it is also First Class if very good.
They travel by night and you save
a hotel night, time, shorter taxi drives between RR Station and City than
airports, and some include dinner,
brakfast even cocktails. I found out that Train Hotels are a great alternative to planes.

The fastest way (if that is what you really mean) is to fly..not necessarily "the best" but definitely the fastest.
By train, there is frequent daytime Talgo service which takes about 7 hours. I have heard from others that the scenery between these two cities isn't all that great so flying may be your best option.