Please help flashing galaxy sl i9003..

I have a samsung galaxy sl i9003 with the stock froyo installed whick came with the phone. I am tired of waiting for a kies update to gingerbread.

so i want to install stock I9003XXKPH(samfirmware) found in this link [I9003][ROM] STOCK ROMS for GALAXY SL I9003 {NOW GINGERBREAD 2.3.4} - xda-developers

But i dont have any idea how to do this. Please help me to install this. any guide or ur own help will be helpful

2 major questions:

1. should i root my phone to install the above firmware. if yes how?

2. will i loose my warranty?