Linux and other unix-style OSs don't use drive letters, they use "mount points". A mount point is how a device or disk partition is associated to a directory on your file system. Once you get used to it, you'll find they're much more flexible and powerful than drive letters.
If you want to see what devices you have mounted on your system, you could use the "mount" command by itself. Or the "df" command, which will also show you block utilization on your devices.
Your floppy device is generally /dev/fd0, and is generally mounted on /mnt/floppy. The "/etc/fstab" file defines the devices and mount points your system knows about by default, so if your floppy isn't mounted, you can probably mount it with either "mount /dev/fd0" or "mount /mnt/floppy".
Remember to unmount it before you remove the disk.
There is also the mtools (mcopy, mdir, etc) package, which allows you to perform dos-like operations on dos floppies without mounting them.
But, since all you really want to do is unzip your VNC zip...why not try the "unzip" command (I'm on a Red Hat system right now, so I can't verify that unzip comes with Mandrake, but I believe so) on the file on your hard drive, and avoid messing with the floppy altogether?