Ok, if you currently are running Windows Me, I assume that when this operating system was setup, all of the space on your harddisk is allocated to Windows Me. If you want to dual-boot Windows Me and Windows XP, you will need to reduce the size of your C: partition to allow you to create a D: partition for Windows XP. (Ok, a partition is a portion of your harddisk space, so for example, if you have a 20Gb drive, you can create two 10Gb partitions, one gets a drive letter of C: and the other has drive letter of D: ). You can use Partition Magic to look at and manage your partitions (Partition Magic has the ability to resize your C: partition whilst keeping your data intact). Ok, still with me? Once you have got two partitions (C: and D: ), you are now ready to install Windows XP into your D: partition. When you install Windows XP I think there is an 'Advanced' button, upon clicking this button there is a checkbox which you need to check called 'choose installation partition during setup', now carry on with the install. Your machine will reboot once it has copied the install files to your hard disk (if you are not installing from the bootable CDROM), when setup asks, you must tell it that you want it to be installed to your D: drive. Hopefully you will then be able to run as dual-boot (Windows XP setup will create a boot menu for you to choose which operating system you want to run).
Ok, I hope this makes better sense, feel free to post a reply if you want more help.
This URL may be of help (mind you the demo download is 40Mb!!!)
http://www.powerquest.com/partitionmagic/pmdemo.html