If you're using a custom recovery tool like SPRecovery or Clockwork, they should block the update if you accept it. Of you don't have one, the update will break root and you can always re-root using one of the methods on this forum; this one will work:
Root Droid 1 - regardless of OS version and it will install SPRecovery if you do the whole process. Then you won't have to worry about breaking root again.
If you want to try and install the update without breaking root, you can try this method:
Installing FRG83D on a Motocache1 rooted Droid
I wasn't able to because my ROM has been modified too much; if you're using a more-or-less stock version of FRG22D, you should be okay.
Your other choice would be to start from root, use a recovery image like above, and then flash a rooted version of FRG83D. You'll have to wipe everything and re-load your apps like with any other ROM, but it's up to you which method you want to try.