I've got this problem with every selection i create using any of the marquee tools. Here's what i'm talking about:

http://img68.imageshack.us/img68/8821/problemeu7.png

Same thing with the rectangular marquee tool. Can anyone help? How do i revert to the default selections? Btw, i've got no idea how this came to pass in the first place.

Thanks!

Make sure this option is checked :

It is, although anti-aliasing is grayed out for the rectangular marquee tool.

and if you use the eliptical one? what happens then?

well, thats what happens when you make a really small selection in a small document.
cause you can't select half a pixel so it approximates.
If youre doing a regular sized selection, then i have no clue.

If you have the FEATHER option set really stinkin high on the rectangular marquee then youll get a rounded selection.