the better way to do this is to log into windows, and give your XP/Vista HD a name that begins with a period, i.e. ".Vista-HD" or something along those lines. os x will read it as an invisible file after the first log in, I believe.
One option is to make an "alias" of your Macintosh HD. Right click your Macintosh HD icon on your desktop and click "Make Alias" then go to Finder > Preferences and remove the checkmark from "Hard disks" under "Show these items on the desktop." Then renamed "Macintosh HD alias" to "Macintosh HD" and move it to where your original "Macintosh HD" icon was.