You may want to check out the
Linux Partition HOWTO and/or do some
Google searches on the differences between different kinds of partitions. There is apparently a legacy hardware limit of 4 primary partitions, but you can create a primary partition and divide it up into as many as 63 (for IDE) or 15 (SCSI) logical partitions. According to the HOWTO, a primary partition which holds logical partitions is called an extended partition. So I guess all you'd need is an extended partition with as many logical partitions as you want to have.
Also, check around these forums and in that HOWTO for the recommended relative sizes of various partitions on your Linux box. You'll probably want to divide up your filesystem into several partitions, instead of using just one, especially if you're low on RAM and need some swap space.