Because it is not documented: On the boot prompt enter after '... boot:' install preseed/early_command=mountfloppy preseed/file=/floppy/flpre.cfgMaybe this is useful for somebody, who cannot create a custom CD or use http.
I tested this with VMware Workstation 5.5, a daily debian-testing-i386-netinst.iso dated 2006-03-29, and a floppy.img.
Helmut Wollmersdorfer