For starters, the bolt pattern on a Yaris is 4 x 100 PCD, so you couldnt fit the alloys.
They also need to be 35 - 40 mm offset and have a centre bore of 56 mm.
Arch work would probably be required to some extent with 17's, definitely if you were planning on lowering the car too. Have a look through the Yaris forum or make a post in it and someone will tell you more. (I drive a Corolla!)

[right][snapback]338819[/snapback][/right]