This is a compaq deskpro, I can't find the specific model number anywhere on or inside the case but it has the following hardware:
AMD Athlon 1GHz
384MB of assorted SDRAM (Tested good with memtest86, let it run for 2 passes)
2x 40GB hard drives (one master, one slave, reactos drive is master)
Nvidia geforce4 MX440 AGP graphics card
What happens is the system POST's normally, and reboots immediately after the "Loading Freeloader" screen appears. To try and narrow this down a little more, i removed the other hard drive from the IDE chain but the behavior persisted.
This occurs on a fresh install so all that is required is to install reactos with the defaults and try to boot. I'm not sure if it will be too useful but i have included the debug log from the install process.