Hi,
While there's probably nothing wrong with Rawrite, I'm just giving you an alternative: I like PartCopy which works very nicely. I have heard about people using MS Debug to do the same thing, but for some reason not many people seem to. I don't know whether that is because there's a problem with it or OS devvers just tend to prefer other utils...
That bit over, let's look at your command line (disclaimer: I guess Debug could overwrite you MBR if not used properly and I am not familiar with it myself, so please double check my command line below before you run anything).
Looking at your command lines below, and firing up help in the Debug program, it says that the format is:
write W [address] [drive] [firstsector] [number]
Thinking about what you want to achieve, should your command line be more like:
-w 0 [drive] 0 1
You seem to supply address=100. I assume this is an offset in to your source file, and you want to copy from byte 0, this should be zero. Next is the drive letter (or number). You provide '0', which I would assume to be the primary hard disk (remember that I am not familiar with Debug, so you may be right on this one). Next, I assume are the sector and length you wish to copy to. I think your parameters here are correct (first sector = 0 (LBA), copy one sector).
Anyway, if the above does not work out, take a look at Rawrite / Partcopy. If you go down the Partcopy route, I think there's a bootsector-copying tutorial on www.osdever.net.
Cheers,
Adam