The OS of your choice.

[kuszmania9999]

i'm using windows xp & 98, don't have problem with it.

[Deerpark]

or to shutdown my computer after a timeout.

Yes then it actually does matter. The shutdown feature is a native windows application, real dos (or even the emulated dos in XP if I'm not mistaken) wouldn't be able to call that command.
But the shell is a native application as well and is therefore able to execute shutdown.

And yes, I know, in the big scheme of the things this hardly matters. But if you're here to learn and want to know more about how windows works behind the scenes, this might be interesting to know.

[Sharamall]

I have to understand what the heck you're talking about to learn anything, though.

[michaewlewis]

That's another part of learning. You have to start with something you don't know.

[Broni]

what the heck you're talking about to learn anything

Since you're here, you're learning already

[SilentAssasin64]

Linux user here.

[patio]

What Flavor ? ?

[SilentAssasin64]

Ubuntu Gutsy.  Gonna try using Arch and Gentoo on a Virtual Machine though.

[tommy gusack]

Win Xp all the way