This is what you have to do:
1. Download Parted Magic iso from here
. The first iso is fine.
2. Burn iso image to CD
3. Boot your computer from this CD.
4. A menu will come, choose the first and wait until Parted Magic (from now on PM) loads.
5. When PM loads, in the bottom of the screen you will see some buttons on a panel. Choose GParted (maybe there's a shortcut on the desktop)
6. When GParted starts, wait until it scans your partitions, and then you will see a screen similar to this
. The partitions are listed and are shown in a visual way. You can right-click on each row (partitions).
7. If you want to delete all partitions (and all data of course) right-click on each drive and select "Delete". Now you have only unallocated space on your HDD.
8. Go to the "Partition" menu and click "New". In the "New Size" section set how big you want your partition. And here's the important thing: Set the "Filesystem" to "FAT32" or "NTFS"! Don't select anything else, because WinXP installer won't recognize any other than these. (The "Primary partition" setting in "Create as" is good, don't change it)
9. Click "Add" button
10. If you want to have multiple partitions (you didn't use all the available space for this partition), repeat step 8. and 9.
11. When you feel that your new partitioning is perfect, just apply the settings with the tick button in the toolbar or with "Apply" in the "Edit" menu.
12. Wait until GParted finishes, and now you can reboot your PC with a completely new partitioning.
13. Put in WinXP installer CD, and go on...
Attention!: when you get to the winxp partitioner tool in the installing process, remember to make a FULL format (on all newly created partitions) and NOT a quick format. It will take some time, but you want to do this if you want to have a proper NTFS filesystem (use this instead of the outdated inferior FAT32) and a more stable environment.
Attention No.2!: Backup all your personal data before doing anything of this!!