If there's no brand name on the case, and no brand name splash screen when you boot the computer, then it could be a custom built PC.
8GB seems like a scary low amount for a HDD these days, but that's actually not horrible for DOS gaming. Most DOS games are gonna only be a few floppy disk in size, so 8GB is a lot. Even Windows 9x games on CD-ROM, pre 3D stuff isn't that large. But still, I wouldn't blame you for putting something bigger in there.
Since new retail PATA drives don't exist anymore, watch out when you're shopping around for one. NOS is always good, but be weary of refurbished shit. A lot of them are pulled from business machines that have a zillion hours clocked on them (you can check the SMART values to see this). They're one foot in the grave.
One option is to get something like this:
http://www.newegg.com/Product/Product.a ... 6822998002Then you'd be all set with a 16 or 32GB CF card, which aren't too expensive. I have yet to do this myself, so I don't know how hard the initial set up is, but I've seen plenty of examples of others doing it.
If you wanna get rid of the 8GB HDD, PM me!