I never actually sat down and did a root...what I did was the manual update, which was posted here by someone. Since then I've been having this loop issue. I have astro and am able to edit this file once its on the SD card, but I'm trying to copy and paste back into system folder (thru astro) but its not allowing me to update my build file. I'm not sure if it has anything to do with the fact that I'm running the free version of astro.
Break down and buy root explorer, do it via command line on terminal emulator or use adb.
If you want to do it command line, open terminal emulator and do the following
mv /sdcard/build.prop /system