First of all check whether your harddisk have enough space to have Fedora 13 also.
Boot from the fedora dvd.
Select the option to install it.
When it comes to partitioning the disks, select custom.
In the available space make two partitions.
On one partition select ext4 as the format as option.
Select the mount point as /.
The other partition u have to select as swap.
The swap partition has to be twice the size of your RAM.
After this you just follow the instructions.
Also don't forget, when it asks for the grub boot loader, select the option as yes.
Just follow the instructions later on.
It will get installed easily. And you can dual boot it with XP.