On my pc with XP I downloaded Oracle Personal Edition and it has been useful. I now have an Apple Mac and wondered if there was a Personal Edition available for it? I have looked on the Oracle site but can't see anything, but maybe it's called a different name?
I assume that if you just got a Mac, then it is an Intel Mac, and not one of the older PowerPC-based Macs. Oracle has only released client software for Intel Macs, but not the full database server software. If you want to run the Oracle database on your Mac, I suggest installing on a supported OS running in a virtual machine (VMware Fusion, Parallels, or VirtualBox). Michael McLaughlin has a very thorough post on his blog about using an Intel Mac as a client for a database server running in VMware Fusion. I suspect that these instructions could be adapted pretty easily for Parallels or VirtualBox, if you use one of those products instead.
The link supplied by am0x will get you a version of the database server that will run on PPC Macs, but I don't know what the success rate of installation is on later versions of OS X, such as Leopard. I don't have any recent experience installing Oracle RDBMS on PPC, since it's been a while since I owned one.
Frankly, unless you're committed to running the Oracle database natively, I'd recommend trying the virtualization approach on your Intel Mac. You'll be able to run more recent versions of the database software (version 10.1.0.3, which is the PPC release, isn't exactly fresh anymore), and I doubt that it will be much more complicated to deploy in a virtualized environment that it would be to work through all the installation tweaks needed to install the PPC version on a recent version of OS X. Just my opinion, though. :-)