Just another update. I think I'll try updating this thread until I get this thing working, then if anyone else has a similar problem, maybe it'll be helpful for them.
Reinstalled and updated to 10.5.8, with no extra video kexts added later. I followed the advice on downloading nvenabler from the prior linked thread. This gave me the same dual blue screen error as nvdarwin. Checking in verbose mode, I can't find any errors though. The only possible error would be Display family matching failed, but from what I've read, this is caused by the OS trying to find the actual mac display, and really isn't a problem at all, as others can boot perfectly fine and don't notice it till later.
When I get the dual blue screens of death, I'm getting yet another weird video error with vertical bars. These disappear after a second though, and it's just two plain displays, with no login window. I've attached a photo, in case this is helpful.
Just in case it was a kernel problem (I'm running Voodoo 9.5.7) I attempted installing without them for the vanilla kernel. This failed to boot.
Adding my device ID to all the kexts generates a black screen on start up when it's added to the nvdaresman.kext. It's fine elsewhere.
I understand that running a different distro won't be much use, but I'm going to attempt two others, just in case. Kalyway and then iDeneb, if I can't get the former working. One is just to see if maybe running an earlier OS version will help, and also to see if maybe different drivers will do something.
I'll keep working on this until I either find a solution, or lose all my hair from frustration.
