Is it possible to create transparent shapes in Photsohop?

[archivedb]

I need to create 100% transparent objects in Photoshop, in this example I create simple shape using Polygon Tool, Normal mode and anti-alias:

dl.dropbox.com/u/14972445/1.png (can't post links yet, 2 more post to go and I'll edit )

Now I create a shadow on new layer below, delete the white background, select my shape using Magic Wand Tool (tried every possible Tolerance with anti-alias and without) and the best I'm able to get is:

dl.dropbox.com/u/14972445/2.png

It's even worse with other shapes, any ideas how to fix the final effects ugly edges? Maybe there's another, easier method of achieving what I want?

[Steve]

You can't post links yet but you "can" post the images here by clicking on the icon on the toolbar.

[ibclare]

Please do; your written description -- as is more often the case than not in describing visual art with words -- just isn't clear. Thanks

[SeniorS]

If you have shape then you don't have to erase it for such effect.
Go to Layer panel and set Fill=0%.