i've been playing around with the posterize layer adjustments in photoshop (been trying to limit the alpha values for a 32-bit image), but when i "save for the web" option with a png24 it doesn't save my posterized version, it saves the full alpha channel. i want to see what the difference in file size may be by limiting the alpha values, but can't if photoshop won't export the changes i've made. am i doing something wrong?

wich photoshop are you using, I'll have to try this in a second and tell you my experience.

Worked Just fine for me... Here's what I did, Your post doesn't really explain much of what you're actually doing.

1: I made one layer with a solid color.
2: made a second layer on top of that one that hade varying levels of transparancy on it.
3: I made the 3rd layer the posterize layer with an amount of 4.
4: click on save for web, and picked png-24
5: I then clicked save, and when I looked at the image with windows viewer it looked just like it did in photoshop

I use CS2 by the way.

i figured out what i was doing wrong, thanks for your tip. i was thinking that if you limited the amount of alpha, the overall file size would go down. but that's not true at least as far as i can tell.