Was the computer a "Netbook" that comes without a CD-ROM? If not skip this paragraph.
Installing Windows XP and got a Blue Screen of Death (BSOD) that said STOP 0x0000007B and now you reboot the computer you get NTLDR is missing?. The issue is "Netbooks" that were all the rage in 2009 were using a technology called AHCI to operate the hard drives, and when Windows XP first came out, that wasn't available. So whatever Windows XP CD you have, does not have whatever AHCI drivers on it to properly install. Fix this by searching the internet for: Install Windows XP (and then type in the manufacturer, like HP or Dell; and then the model number, which will be something like nc4000) and hopefully you run across another friendly corner of the internet like this one that describes how to use programs like nLite to "slipstream" in the AHCI drivers and make a new Windows XP CD. Doing all that is somewhat advanced. I wrote up an install for HP Minis in 2010 on GDGT but with age comes broken links and it can only be used as a guildline to find what you are looking for.
The other option, is jump to Win7, I've come across a great YouTube videos about this recently:
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