I too would recommend VirtualBox if you are only doing this to get a taste of the different distros.
If you really want multiboot, the general procedure is:
1. During the install of the first distro, partition the disk so there is room for each of the distros you plan to install (eg 10Gb+ each). They can share a swap partition (since only one will run at a time). Some people also create a data partition that they share between all the distros.
2. During the partition phase in the subsequent install of other distros, make sure you only format (and set up the mount point '/') for the partition you want to use.
Many of the major distro installations will set up grub for you, automatically detecting all the previously installed operating systems and creating an appropriate boot menu list. Perhaps install more obscure distros first (in case they don't do this); leave a major distro like Fedora or Ubuntu to be the last one.
Last edited by neonsignal; 08-17-2009 at 10:08 PM.