Hey Arachkid,
Great that you build your own computers, however Sillygirl said that someone built the computer for her, so she doesn't know if the cpu/ram/video/etc was at default settings or oc'ed and if so by how much, when I build a computer I usually set the bios to aggressive after the install is complete. I've had problems on a couple of rebuilds when it was aggressively overclocked, the solution was to reset bios to default, while this was more of a long shot it was a possible solution.
Hey Sillygirl,
Another few possiblities, if you've already partitioned and/or reformatted the drive, try rebuilding the master boot record, you do that by boot disk, then typing in fdisk /mbr, second I would try a third party installer like 98lite, it works very well for a clean install, it will copy the necessary cab files to the hard drive before starting a windows install, this will let you know if the cd files are corrupt or at least it should. Another benefit of this is that you can delete these install files and then put your swapfile there, its the fastest part of the disk, make sure that after install you turn off swapfile, reboot, delete install files, enable swapfile for the size of the deleted install files and it will automatically setup over the deleted files.
Other possiblities are that your psu is failing, not having enough power can give your hard drive fits and corrupt your data especially on start up. Overheating can corrupt files as well and crash your computer. Are you overheating someplace? Do you need to blow out all that dust? Is all the fans working?
Anyway I'm out of ideas at this point, maybe if you give additional details someone may come up with a solution.