VAG COM is some software you can plug into your OB1 port (infront of your gear stick where you put your SPS) so you can view what you car is doing via a laptop. You can also clear fault codes, change a few settings and most importantly you can log boost fueling etc.
You can get the correct cables from Ross tech at anout £125 or from ebay for about £20 and get the free downloads
hope this helps
Scott