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I use Terminal Services to manage that computer if it has Windows Server on it, or Remote Desktop Connection if it is a Windows XP machine.
You just need to make sure the BIOS by passes the "Error on Keyboard" at boot up.
I'd go for cheap software solution like RAdmin
In my experience, if the computer is co-located, it's best to go with KVM. There are security issues with Radmin (even though I do use it to REMOTELY admin our computers) and if it's right there, you can get a good cheap KVM switch for around what you'd spend on Radmin.
Radmin has good uses, but can still be really slow even if co-located when doing any graphic design... and forget about any kind of video streaming with Radmin.
Plus, some computers (if the BIOS is not set right) will not boot the computer if there is no keyboard attached. If the power goes down, or you do a Radmin restart, the computer won't come up again... then you've got to switch all the cables around again.
If you go with Radmin, make sure to adjust the BIOS to not halt the boot if the keyboard fails, and be sure to lock the computer down hard with a firewall.
Good luck!