http://android-dls.com/wiki/index.php?title=OTA_Updates#Cupcake_1.5
drop this on your SD card
1)turn ur phone off boot it holding the home button
2)when you see the triangle hi alt+L
3)then alt+S
4)Press home and back when it tells you to (to reboot ur phone)
5)you'll notice it says installing Radio after you hit hom+back (thats normal and fine)
6)youll see it reboot like 2 times then youll see the new android loading screen. and there ya go! android 1.5 without having to root/jailbreak and ur good to go.