I wish I had better news, but there's really mot much you can do 😟 The reality is that the MBP has a different LCD display than your PB, with different properties. Native resolution is intrinsic to an LCD display - each model has it's very own native resolution and that cannot be altered (that's why it's
"native", of course).
http://en.wikipedia.org/wiki/Native_resolution
Literally, the only way you could get a 1440x900 display in your current 17" MBP would be to physically transplant the display panel from the PB into the MBP (I'm really not even sure that would work).
Your choices are:
1) give it time and try to adjust to the 1680 x 1050 resolution of the MBP
2) set the display to a non-native resolution as stated above, and live with the 'fuzziness' of the display; as stated above, you can use System Preferences for 1440x852, which I'd consider 'pretty darn close to 1440x900), or the 3rd party utility to get 1440x900 on the dot, but because neither of those is the 1680x1050 native resolution of the display, it will look 'grainy'
3) sell the MBP and keep using your PB
4) consider a 15" MBP, which has a native resolution of 1440x900 (but the display is smaller, and the pixels are correspondingly smaller, compared to your 17" PB)