Min 3 gigs but I would go with at least 6...
windws recognizes the size of a gigabyte differently than the manufacturer...It is standard for the "recognized size of drive to be somewhat lower than stated on drive...you can search forums for more info...but not important.
fdisk is a dos command that runs a program that can delete and or partition your HD.
you'd have to boot to a command prompt and type in FDISK and follow directions....can be confusing for a first timer.
I would use a program like partition magic to do it after the fact.