The problem I'm having with Nero is that everytime I want to add something new to an already burnt on disc it tells me it's going to have to trash what's already there. I don't want that. All I want to do is add to what's already there. Can somebody please tell me what to click inside of Nero to tell him he's being a bad boy and not to do that anymore?

whether you can write to a disc that already has data on it or not depends on how you burnt the disc. if you create a multisession disc, then you can write more to it but you have to import the session then write to the disc. otherwise, normally, the discs are burnt as single session.

As spacesurfer already suggested, it sounds like you've already written the discs as single session, thus nothing you can do there. Just write future disks as multi session. Beware though I've had some intermittent problems in the past reading the older data on multi session disks. I think its something up with my writer but still worthy of note I reckon.