you are not really suppose to install both, but before i had nti cd maker, nero, adaptec easy cd creator, clone cd, and blind write all installed. I never had a problem.
The only way to know for sure is try it if you want. Personally I would just use nero.
You might want to backup your registry first before you install them.
Kind of like this
backup regisrty first
install roxio. don't install direct cd unless you really need it.
then if that works ok, backup the registry again.
then install nero and if everything is fine backup the registry one more time.
There is also a special way to select which burner software controls the system when the computer loads.
Safest way would be to just install nero.