Yeah, I had to do the same. To be safe, I deleted everything on the OS X partition that had to do with Toast before running the 5.2 update (I left a bare-bones 5.0 install on my very tiny OS 9.2 partiition). It looks like this is what you need to do in order to get Toast 5.2 to work correctly - or at all.
You'd think that Roxio would mention this (at the very least - seeing as they can't make their installer trouble-free), but no. I do like the Toast app OK but, damn, Roxio's support is just terrible. Figuring out trying trashing all preferences and .dat files are no big deal for us savy Macrumors-types, but I can imagine the frustration that is occurring as we speak, as the majority of Toast users are attempting to update and all they get are crashing and error messages - with zero help and assistance from Roxio.
Not a good way to run a company, but seeing that Toast really has no competition on the Mac platform, well, of course they get away with it. I always thought that a fully loaded CD/DVD burning suite would make a great iApp. And probably not too difficult for Apple to create, seeing as the basic components (Disc Burner, Disk Copy) are already present in OS X. Not that I expect to see this, but it would be a nice alternative to Toast.