Some versions of windows will require additional tweaking.  What is
your OS?

For me, in win2k, I renamed the directory which was unzipped to "ant"
and put it in C:\, then did the environmental variables as you have.
Additionally, in Path I've got the explicit value of ANT_HOME appended
because if Path is before ANT_HOME then Path can't know what the
ANT_HOME value can be.

what happens when you just type "ant" at the c-prompt?

here's my output:
Microsoft Windows 2000 [Version 5.00.2195]
(C) Copyright 1985-2000 Microsoft Corp.

C:\Documents and Settings\Administrator>ant -version
Apache Ant version 1.6.2 compiled on July 16 2004
C:\Documents and Settings\Administrator>

--
Thufir Hawat