Booting DOS or other os's then partitioning and formatting the drive before installing XP. The cause is someone didn't answer YES to large disk support.
However, I never bother with such. I boot my XP CD and use it to delete the old partitions, create new and let it install proper. If an upgrade version it will ask for the qualifying CD later which I let it see.
I have a DELL Inspiron 8000. I put in a new hard drive (Western Digital) 40 GB. I re-installed the CD's that came with DELL Inspiron 8000 and the Windows XP upgrade. When done, the system shows and thinks it's only has 2 GB. My last hard drive I had in my system was partition. And it read the same. Is there something in my BIOS that needs replacing?