HARD PLASTIC: Now, this time there will be
no clickable thumbs or onmouseovers. This is a short and easy tutorial,
so I'll keep everything as simple as possible. This time you'll be best
off using Photoshop 5, as everything will be made using PS effects and
filters. Don't worry: everything can be duplicated by hand, using the
airbrush and standard tools. I would say this technique is best suited
for web and interface graphics, but hopefully you'll manage to apply what
you learn to textures and such as well.
SHAPE UP: Create a new layer and
draw a shape, any shape. Rounded edges show off the highlights very well.
I ususally fire up Freehand or Illustrator for things like this, but the
paths in Photoshop (or even polylasso tool + Select- modify - smooth)
do a good job at this.
EFFECTS: OK, time to add some threedimentionality
to this. I applied these effects:
Inner shadow:
Opacity 85
Angle -48
Distance 5
Blur 18
Intensity 184
Drop shadow:
Opacity 75
Angle 120
Distance 5
Blur 10
Intensity 0
Select your shape. This can be done by CTRL-clicking in the layers window,
but I think "Select all (CTRL+A), nudge up, nudge down" is more accurate
and also faster to pull off.
Select-Modify-Contract-7px. Layer via copy (CTRL+J). 
Now you've got a new layer with the same shape as the original, but smaller.
Color it white. Please don't use the airbrush, just ALT+BACKSPACE to fill
using foreground color or CTRL+DEL to use background color. Photoshop has
unfortunately got very few keyboard shortcuts... at least try to memorize
the ones that are supported.
Select yer new layer, offset it slightly 
Cut (DEL). Now we've got a highlight. Doesn't look very good, now, does
it?
After a gaussian blur we are getting somewhere. 
FINISHING TOUCHES: Here I've changed the position
of the highlight slightly, decreased opacity, and used the eraser tool to
smooth each end.
DERE...DUN: Add some junk, and that's it. Basically
what you've got now are some basic ideas about highlights and shading.