No update is forced on you.
ALL updates are optional. You do not have to update. It will not update without you selecting to update.
Updating itunes does not change your playlists or erase music, unless something has gone very wrong.
If it does go wrong, then use your backup copy of your computer put everything back.
I actually agree with you here: this update WAS forced for me too: a dialogue box came up saying that my current version was corrupted or not installed correctly. iTunes wouldn't open for me unless I reinstalled. Which I did, but now when I click "Sync Music" I lose everything. (I obviously haven't synced anything since I reinstalled.) But even though I haven't synced, half of my library is missing. (106 songs and 14 whole albums) But all of my music is still saved in my iTunes folder? Nothing makes sense!
And what do you mean roaminggnome to use "my backup copy of my computer"?? I'm not sure what you're talking about...