This SHOULD be easy ..... I can switch from booting X to 9 in the system prefs-> start up disk. Once I am running 9 how to I get X to boot again? I must be slow, cause I can't figure this one out for some reason.
You should be able to just open System Prefs->Startup Disk, click on the 9 folder, then click Restart. To change back, use the Startup Disk control panel in 9.
However, it's worth asking what Mac you have. Some newer ones can't boot into 9.