I know that they are already slightly transparent, but it is such that they may as well be solid... If you are not paying attention, you just can't see it in most lights.
It is a shame that there is no way of adjusting the opacity.
Can't help you with the menu, but heres a tutorial for windows themselves.
you need a property list editor, or a lot of experience with the terminal and VI. (this is where us OSX users with linux history shine).
the files are
/System/Library/Frameworks/Foundation.framework/Resources/NSCoreSuite.scriptSuit
.../Resources/NSCoreSuite.scriptTerminology
You want to create a new Child process under Classes/NSWindow/Attributes/
and call it "alphaValue" (as i've done in the image), expanding it will reveal three properties; Apple Event Code, Class, Read-Only.
set the Class to "NSNumber"
the Apple Event Code to "alph"
Read-Only: No
should look like that.
Now, open The NSCoreSuite.scriptTerminology file
Again under Classes/NSWindow/Attributes/
Create a new Child called "alphaValue"
this time the three preferences are Description, Name, Attribute Gender.
set them as follows:
Description: The alpha value of the window
Name: alpha value
Attribute Gender: none
Save both Files.
now you just need to write an apple script to set the windows.
heres the simplest one yet (30% transparent),
in File: safari.scpt
tell application "Safari"
set alpha value of front window to 0.7
end tell
here the final product, running in apple script editor
you can get quite advanced with it, setting transparency based on foreground/background (like in SetAlphaValue), or just based on application (which would mean every application if desired). it would also be possible to change the menu opacity like this (possibly with another UI framework change), haven't desired it.
hope this helps, but either way, enjoy
Test/Pictured MB373LL/A Macbook Pro
Core i7 2.66Ghz
OS-X: 10.6.4
Pictures used for education purposes only