[mgol]

When I try to boot OSX, the Apple symbol comes on, but not the little spinning gear.
If I boot from the OSX install disc and switch the startup disk to OS9 (classic) then restart, my computer works as it used to, but I can't get it to restart in OS X.
If I reinstall OS X.1, and don't restart, I can use Mail, but not Safari.
Any suggestions?

[Cadaver]

What kind of machine is it, specifically? There have been many different dual processor G4 models.
Is the machine upgraded in any way? Be specific.
Are there any firmware updates for it (check Apple's support page for your machine) that should be installed before attempting to use OS X?
Consider reformatting your hard drive, and consider doing a low-level reformat. Takes longer, but may help clear out any bad blocks that have developed.
Are you really trying to install OS X 10.1?? I suugest something a bit more modern such as 10.3 or 10.4. Version 10.1 is really quite obsolete at this point.

[Madrag]

I also have a G4 (don't know your specs), but I also had problems with 10.1...

Follow Cadaver's suggestions, and maybe you should consider dumping OS 9 altogether, as it may be the reason you're not able to boot in X (depends on the way you've installed both OS's)