Can I Use My Computer On An Extension Cord?

[superstar]

I have one of those basic white extension cords lying around. It's rated at a max of 1650watts. My computer has a 460 watt power supply. Do you think it would be safe to use it on the extension cord? There's no ground wire in any of my house walls because the home was built in the 1920's, although the interior looks modern, and does have the third ground prong on the outlets. So plugging it into the extension cord with an adapter would pretty much be the same as plugging it into the wall.

Thanks