Can u buy parts and take it to the dealer for install? Or do you have to buy from them to have them install?

I would think that would be up the the individual dealer. Also may make a difference if the part is "approved" by Scion, such as the AEM CAI vs a Weapon R intake, I would just call dealer and let him know what you had in mind. Good Luck.

i asked about this as well in order to KEEP my warranty on certain thing and they told me NO!...
they said the only way anything was under warranty was if i had purchased the XB new with the parts already on it at the time of delivery.

That is a surprise. Don't think it says much for their faith in their service department though.