the main things you need to look at when buying alloys is:
the centre bore, can be anything from 57.1 and over (you can use spigot rings to get a proper fitment)
the PCD should be 4x100 (i.e. four bolts with the inner diameter of 100mm)
and an offset of between 35 and 38 to get a perfect fit without rubbing or the wheels sticking out of the wheels arches,
you can get up to 17's with 205/40/r17 tryes without any modifications to the wheel arches...thats what i have, any bigger i think you have to reshape the arches
most of the older golfs and polos have the same fittings which can
help when when searching for wheels...or you can look at multifit wheels...
hope this
help 