Tray Disk Free will display numerically (unique to this program as far as I know) the free space of your hard drive on system tray bar, and can use of a few command line options.
LiVista Rescup is a program that you can store on a USB pen drive or floppy disk and run from within the Vista Setup. It will automagically load a nice environment (with taskbar, explorer etc.) you can use as a rescue system.