i am faced with the same issue. there is a "switching box" type of thing i've seen that is basically a white box with inputs on the back and output on the front that should allow you to do this, and it has a black dial on the front that allows you to switch between inputs. i don't think ocuk sell them so i can't say where to get it from as i think they are a competitor. i seem to remember these things being used for sharing printers etc.
i'm pretty sure it will work, however i don't have the cash to buy it until the end of the month (it's not expensive) so i can't test it. such a thing does exist though!
the sticky gives info about the vga monitor cable, but not about the means to have both a pc and 360 hooked up to the same monitor at the same time, so you can switch between inputs without unplugging the cables (not when i last looked anyway).
nin9a