questions about the 15" stock Alloy wheels

[songa]

hey guys, i got a 2009 yaris with the stock 15" steel wheels that came with the convenience package. i believe they are these specs:

* Wheels: 5.5JJ x 15 Steel Disc

* Tires: P185/60R15 AS BSW

i also believe the stock 15" alloys that come with the S trim are the same exact size. heres a pic of the alloys im talking about:

http://z.about.com/d/cars/1/0/O/Y/to...is_s_wheel.jpg

if i just replace my existing 15" steels with those, what differences will i notice? how much do the 15" alloys weigh compared to the 15" steels? also, since they are the same size specs and everything, it shouldnt affect my odometer/speedometer readings or anything, right?

lastly, is there any place online where i can buya set of these? thanks!