Actually, you don't even need an ASPI layer installed anymore. I've had tons of problems in the past trying to install ASPI layers on 2000/XP. It's not needed, so why bother? Many programs don't need it, and for those that do, there's a simple workaround.
For instance, one of the files that gets installed with Nero is "WNASPI32.DLL". This file in the Nero directory is all that is needed for it to work correctly. The last few versions of Cdrwin (the good, original Cdrwin up to version 4.0, not that crappy new 5.0) also come with the "WNASPI32.DLL" file.
For those programs that say they need an ASPI layer and don't run correctly, just copy this file into their directory. They should start right up.
You should uninstall the programs you currently have, and clean the registry like NetLion suggests, but then just reinstall Nero with no extra ASPI layer...it'll work.
Take care,
WeRD