Alternator replacement?

I have a 1999 V.W Transporter 2.5 tdi, the alternator has now packed up twice in a little over 2 years. Is it a big job to replace it myself, are any special tools required, and a rough estimate of the time involved would be appreciated. It looks kind of difficult to get to. Any idea of the price of a brand new rather than reconditioned one and where's the best place to get one from.

Many thanks.