you have to install bootstrapper or safestrap, safestrap is the better option I believe. then boot into recovery wipe data/cache/dalvik and install the zip. have u ever flashed a rom before? if not read up on it a little before u do it. there should be directions in the all things root guide in the sticky above.
Flashing .904 was simple haha and after reading instructions I realized they were quite similar. A ROM does have a few more steps involved. I used safestrap and flashed Eclips 2.2. Honestly, I love it!