Read the docs I mentioned, things'll get a lot clearer after you read them.
Don't let Partition Magic set the partitions, just clear off some freespace. The linux installer of the distro you want to use will set up the partitions for you, using linux tools like fdisk or cfdisk.
You'll need a partition for either lilo or grub in order to get your boot menu, to select windows or linux. (Don't use Microsoft's tools - they deliberately screw up other oses)
If you want a swap (not necessary, linux doesn't need a swap like winblows - especially with 640mb!
), you need a partition for that. Linux also requires a separate partion to boot from. That leaves the partition for all your data and executables. [img]tongue.gif[/img]