Port 21 open
With only FTP open you will have a tougher time. If you have administrator rights you could still copy an executable into the correct directory - see 1, but you will not have the ability to reboot the host - you will have to wait until someone reboots it. You might want to try a D.O.S attack on the machine, but usually it will just hang (which is suspect, but will speed up a manual reboot). If you do not have administrator rights chances are slimmer - you need to upload a Trojan - again, be very careful what you upload - most machines nowadays have virus scanners. You could try to wrap netcat as something that the administrator will be tempted to execute - you know the drill - pamela.exe or whatever. If you do not make use of a known Trojan and there is no way for your custom Trojan to let you know that it was executed you will need some mechanism of checking if the program was executed - a (local) netcat in a loop with mail notification perhaps?