I used the eliptical selection tool to make some shapes and fill them and stuff, (I am redesigning my website), but now it is jaggies galore! Is there an easy way to antialias them or something now that they are already made? or to prevent them from being jagged?
well you can blur the shapes slightly.....or if you have PS 6.0 use vector shapes(but you can do the same thing in earlier versions by using clipping paths(which is what 6.0 is automatically doing anyway).
Or make the image larger than what it is intended for and when your done resize it.
Upping the resolution isn't the solution; you simply need to have the "Anti-aliased" box checked in the Marquee Options window. If you're building these images strictly for web use, then 72 dpi is right where you want to be.