What are you trying to do? did you break your turbo on the 1.9TDI? if its the same engine then yes it will fit (provding the engine code matches with yours and the Altea). Same example for BWA (leon, golf, a3...)
 
why are you going to buy the turbo from Seat? we use ITS Turbo's in Bradford/Dridlington and they seem pretty good, try them...