I just wish I could have embeded the theme song.
Only thing you could try is to repartition the drive..... Is this a 40 GB drive, or just a 40 gig partition? According to my calc 40 GB drive should be 38.1 real GB. 37.9 Isn't so far off that mark, .2 could account for just bad sectors. Thats drive though, 40 gig partition would be something else.
As for the different sizes you've encountered, I have encounter different sizes within windows, depending on what program or script is looking at the drive.
If it continues to shrink though it could be having a bad head, causing write or read errors that are mismarking good sectors bad, thus decressing the size...... I'd think this would happen slowly though, and not all at one.... I've never heard of anything like that ever happening though.