I'm assuming you have unlocked bootloader, if not, check this tutorial by lollylost- link
download fastboot with usb drivers from here - link
1.) download kernel and rom you want to use
2.) copy rom zip in SD card
3.) copy kernel in fastboot folder (kernel is an .img extension file usually named as boot.img, if it is not boot.img then rename it as boot.img)
open command window in fastboot folder ( hold shift, right click on background of folder and click 'open command window here)
4.) connect your phone in fastboot mode (by holding volume up key and connecting usb)
5.) on command window, enter 'fastboot -i 0xfce flash boot boot.img' without quotes.
**by giving above command, you will flash kernel.**
6.) enter 'fastboot -i 0xfce reboot' without quotes
7.) now your phone will reboot, when booting, press volume down key 5-6 times when sony ericsson logo appears, you will enter recovery
8.) choose full wipe/ factory reset in recovery
9.) choose wipe cache partition in recovery
10.) choose install zip from SD card, browse to rom zip file and install it
11.) when done, choose reboot now.
now your phone will have new rom
side notes- navigation in recovery is done by using volume keys to scroll, home key to select and back key to go back
Edited by shapeshifter, 09 February 2012 - 06:49 PM.