I successfully did a HD window mod, after a few rounds of trial and error.
The hardest part was getting the hard drive opened and sealed properly. I found that plastic wrap was annoying and difficult to seal the hard drive with because if you aren't careful, the plastic will touch the platter and/or write/read head. That's a no no. That ruined one of my (crappy, thus an early candidate) hard drives.
I found the best way was to use a tupperware container. I meticulously rubbed it down the tub and lid with a tack cloth (used for prepping a painting surface, and available at all hardware stores). After I sealed it up, I shook it up to get the dust moving, and let it sit a while to let the dust stick to the tack I left on the sides.
I used the bathroom method to create a clean room. I removed all but two of the screws from the hard drive, and then went into the bathroom. I quickly removed the other two, removed the cover, and put the drive into the container. After sealing it, I left. This minimizes the chance of it becoming contaminated with moisture.
It took me three hard drives to figure out this ideal method for myself. Luckily the first two were crappy sub 10GB ATA33s, and my third one (the one that worked), was one of the only spares I had, a 40GB ATA66.
You don't need a vacuum chamber for the hard drive; you just need to keep it away from dust and other contaminants.