Root Updating to 2.2.1 with custom recovery - Noob

[robert_e_leet]

I'm pretty newb when it comes to Android hacking and adb so please excuse my ignorance.
I bought a nexus one from someone off craigslist and it was already rooted and has a custom recovery RA-nexus-v1.7.0.1 installed.
I currently have FRF93 installed but my phone keeps harassing me to download the OTA 2.2.1 update.
Of course when I try to install the update it gives the standard verification failed and I'm assuming I need a custom update.zip like I needed when I upgraded to FRF93.
Any help/suggestions would be very very graciously welcomed and appreciated

 

[Rusty]

Change your custom recovery to one that doesn't check signatures such at Amon RA 1.8 (or above) or ClockworkMod.

 

[Teknologic]

If you don't know anything about how to do that, then the simplest way is to download ROM manager from the market and simply select the option to flash your recovery from there