It depends on your hardware and how your BIOS is configured.
Intel have ‘vPro’ which allows you to do what you want. (remotely change boot order)
[url]http://en.wikipedia.org/wiki/Intel_Active_Management_Technology#Using_Intel_AMT[/url]
[quote]Remote boot the PC by remotely redirecting the PC’s boot process, causing it to boot from a different image, such as a network share, bootable CD-ROM or DVD, remediation drive, or other boot device.[1][7] This feature supports remote booting a PC that has a corrupted or missing OS.[/quote]