What does "missing" mean?
When you did the re-install, did you delete the existing partitions or install over the existing installation?
What size is the hard disk? What proportion is the 8GB? It is pretty normal for the partitions on a disk to add up to less than the theoretical maximum. Also, there may be a hidden recovery partition.
If you want to maximise the chances of recovering your data, you should stop right now and buy a replacment hard disk and an external USB HD caddy.
Take out the existing HD, put in the new, install XP, put the old disk in the USB caddy and try an recover your data.
SD