Using the ALT key in Windows with Parallels I need Windows for my development environment on my Mac. I use Alt-U and Alt-S a lot in this software. I can't do this on my Mac. Is there a way to send the Alt key presses to the virtual machine? 

Alt-U shows the Accessibility Utility Manager. Pressing Alt-S just types an "s". At work on Windows XP, neither of these behaviors happen.
I was able to get the desired effect by holding down the ctrl+alt keys, then releasing just the ctrl key to use the alt function.

Hurrah! No editing keyboard preferences required. Hope this helps someone else too.