Here is a first (easy) try:
For the Hal.dll file missing problem do this:
1.Insert and boot from your Windows XP CD.
2.At the first R=Repair option, press the R key
3.Press the number that corresponds to the correct location for the installation of Windows you want to repair.
Typically this will be #1
4.Type bootcfg /list to show the current entries in the BOOT.INI file
5.Type bootcfg /rebuild to repair it
6.Type exit and take out the CD ROM
The problem is the BOOT.INI file on the root of the C: drive is misconfigured.
If this doesn't work we can find a guide to copy the file from the XP disk.
This is assuming that you have an XP CD provided by HP.
If not then you are limited to their recovery procedures which should be found in the manual or on their web site.
http://welcome.hp.com/country/us/en/support.html