Unscrewed it. Those 8 little panels on the bottom hide screws. Then I just sat the insides in a relatively safe spot, and painted everything. (Put tape over the serial number and other info on that sticker in the back). Expansion slot cover, fan cover, even the thing that the power cord slides down into.
I'm sure Krylon makes red paint, and it's pretty good stuff for that cheap. I like my white PS2 better than my blue metallic PS1, which costed $4.
You just have to make sure that when you do it, you have a good ventilated room, or the wind isn't blowing hard outside, otherwise your paint job will look crappy. And work in coats. First coat shouldn't even cover it all, then wait 5-10 minutes, do a second coat, etc, otherwise you can get runs which look bad (I've got 2 on the top, but 1 is covered by the MotorsportsDecals.com sticker, and the other isn't noticeable).