boot from the floppy and then, when you have access to your linux system, simply reinstall grub..
installing windows almost always destroys other installations' bootloaders
it's commong knowledge. to avoid this, grub ought to be installed into a partition and not in MBR, and when installing windows, set the active partition to where windows is (otherwise active partition is where grub resides). this makes windows overwrite only itself and MBR, but leave the grub-partition alone..after it's done, simply switch the active partition from windows to grub's partition, and linux works again. simple