I hope that you didn't copy the file to the floppy...
You need to use a formatted floppy, and with the .exe file on the hard-drive double-click on it and it will make the bootdiskette for you. Same procedure for all bootdiskettes made from image files.
You should be able to get to a prompt and type delpart and when you need to delete a partition press the DEL key.
Sorry, I should have added more info.
When you boot to the diskette you should see a screen which lists your CD drives and it should say press any key to continue.
At the prompt type: A:\>dir and press Enter to see the DELPART directory and all of the other commands available on the bootdisk.
You need to get into the DELPART directory so type:
A:\>cd delpart , where cd means change directory. You'll now see:
A:\>DELPART> , and you should type A:\>DELPART>delpart and press Enter.
The Delpart GUI (screen) should now load with a DIRE warning!!! ... press Enter.
You can then see the partitions on your drive. Delete them in reverse order deleting the C: boot partition last.
Now you should be able to re-start and boot directly to your Windows 2000 SP4 CD.
If your CD does not have SP4 then it should be slipstreamed usiong AutoStreamer 1·0 (freeware) so as to incorporate the service pack and so that you save time updating.