Welcome to the forums. By “it” I assume you mean the computer. Yes that’s easy. If you use Ubuntu use Gparted to make a partition for Windows XP. There are number of ways to set up the appropriate partition. What I would do would be to make a 100 MB primary partition at the front of the hard drive. Then after the Ubuntu partition make a partition of 18 GB or more after the Ubuntu partition. The 18 GB partition can be either primary or a logical partition in an extended partition. It doesn’t matter. The boot files that Windows XP needs such as ntldr and boot.ini will end up in the 100 MB partition.
Insert the Windows CD and reboot. Install windows XP into the partition you just made for. Then install easy BCD in Windows XP. Then see step three in the Ubuntu documentation below for making nihilist entry for Ubuntu.
Setting up a dual boot between Windows XP and Ubuntu only uses the automatic configuration choices in Easy BCD. When you go to add the Ubuntu selection you don’t even have a chance to select the partition a drive letter that it’s on. Easy BCD will pick it up automatically.