It’s possible to install Linux on your Mac instead of Mac OS X. While this might make some sense to long-time Linux users who just want to take advantage of Mac hardware, for most of the people it’s much more interesting to use Mac OS X as the working operating system.
Yet, even for a pure Mac user it can be helpful to have more than one operating system at hand. With Microsoft’s Virtual PC (you know, the emulation program that many people use with Windows XP to do their online banking 
) you can install a free version of SuSE Linux. This might be useful for testing purposes (for web designers, programmers, you name it).
While the installation of a Linux system instead of Mac OS X is described in the O’Reilly book Mac OS X Hacks you find few information on installing Linux within Virtual PC. Here is some help:
On the SuSE page you can choose to download installation files for PowerPC. Because Virtual PC emulates PC hardware, you have to work with the i386 version instead. The manual to install SuSE on a PC can be found here.
Now create a new virtual PC. Notice that the virtual disk is a sparse image, meaning that it will grow in size with the files you copy into it later. Choose to share one IP address with your Mac, as the function virtual switch can be problematic in rare situations.
Afterwards download the image file ‘boot.iso’ to your Mac and burn it on a CD using disk utility (in Panther) or disk image (in Jaguar). The file can be downloaded here: ftp://ftp.suse.com/pub/suse/i386/current/boot/boot.iso
Put the CD in your CD drive and start the new virtual PC. The installer starts and needs configuration to download some files from the net. Load the driver modul tulip: DEC Tulip (DC21x4x) PCI, because Virtual PC emulates an Intel DC21041 Ethernet card.
The assistant needs the IP address of a SuSE server. Ping the server in your country and enter the returned IP address in the IP field. The current address of the german server is 195.135.221.130. The path to the download directory is /pub/suse/i386/current/.
In one of the next steps YaST2 needs to partition your virtual disk. By default it seems to take the whole free space on your disk and divides it into two pieces. You can’t reduce the size of the disk, but you can reduce the size of the partitions.
If you take 700 MB for the swap partition and 4 GB for the system (root), you have enough space for the standard installation. Don’t be afraid, the installer won’t use your whole disk, it will only take about 1.7 GB.
Now you can start the installation. The installer will take some hours to download the necessary files and to install them. After this answer YaST’s questions (answer yes if you are not sure) and you are done.
Now you have a free version of SuSE Linux running within Virtual PC on your Mac.
This is a good chance to see that Apple did an incredible job merging Unix with the simplicity of the Mac.
Please be aware, that you try this tip on your own risk!