I've been reading around about this error, and I couldn't find the exact error as mine, so I'm gonna try here.
I just purchased a new memory module of 1GB. I have an old Gigabyte motherboard (945P-S3), with 4 memory slots. I previously had 3 modules (2GB, 1GB and 512MB), when I added the new one I got BAD POOL HEADER while booting windows 7. I thought the module isn't working, but when I moved it in the place of the old one, it worked. Long story short, I tried all the combinations and all the modules and slots are working, but only when there's only 3 modules installed. 4 modules in any combination result in said error.
Please, any advice is welcome?
PS I also noticed that I have only 3,25GB used whichever modules I install (3,5GB or 4), but I assume it has something to do with win7, graphics or sound card.