I assume you mean your data files, that is, files you have created yourself.
Usually, you don't need to do a full system backup since you should have
install disks for your operating system and applications.
You can image the entire partition if you have a place, a separate partition
for example, to store the image file but you would need third party software
such as Drive Image,
www.powerquest.com for this purpose.
You can simply backup your data files as mentioned above, you can copy them
to CD if you have a CD writer or, if you don't have too many and they aren't
too big I suppose you could copy them to floppy disk.
XP has a backup application which in XP Pro is installed by default but in
Home Edition must be installed manually. Assuming you have an XP CD and not
a customized OEM version you can install XP backup as follows:
Go to the valueadd\msft\ntbackup folder on the XP Home Edition cd and
install ntbackup manually by double clicking the file.
You will need to backup to your hard drive using the above application and
then copy the backup file to other media or to another partition.
There are many ways to do what you want to do. You can select the files in
explorer, right click drag them to another location, partition, CD, etc. and
select copy from the menu when you release the right click or you can use a
backup application as specified above and choose the files you wish to
backup or you can do a full image as specified above. A lot depends on the
media you have, it's capacity as that determines its ability to hold all the
files or a single large backup or image file and what it is you wish to
backup. Unless, you are restoring an image, you should never restore a full
backup as opposed to just your data as that backup likely contains the
problems you are trying to resolve with a format and reinstall. Hence, you
reinstall the OS, reinstall your applications and then if you happen to have
done a full backup, you select the files you wish to restore from that
backup individually.
Hope that helps.