The XV Crosstrek is a vehicle. Are you asking if the wheels from an XV Crosstrek will fit an '03 Forester? Google tells me the stock tire size for the XV is 225/55 R17. A forum search tells me the stock tire size on an '03 Forester is P215/60 R16.
You can use this website to compare tire sizes. A few extra details of what you're asking may help as well.
Simply put, yes. The wheels are a 48 offset, same as the Forester and the tire size as mentioned previously will fit in the fender well no problem. Somewhere there is a post where someone swapped wheels (they own a SG Forester and XV), looked OK.