I just checked out everything from the jakarta-lucene CVS and tried to 
build it. I'm running on Win 2K and using Sun JDK 1.3.

The first problem was that the lib directory includes ant-1.3.jar but 
does not include the optional.jar file. I had it in a separate ant 1.3 
install and after I copied it into the lib directory that problem went 
away (I also tried setting ANT_HOME as the error message suggested but 
that didn't seem to help).

After that problem went away, this is the problem I'm running into:
==================================================
K:\projects\opensource\jakarta-lucene\jakarta-cvs>build
CLASSPATH=".\lib\jakarta-ant-1.3-optional.jar;.\lib\velocity-1.2-dev.jar;.\lib\junit_35.jar;.\lib\jdom-b7.jar;.\lib\ant-1.3.ja
r;.\lib\xerces-1.3.0.jar;"
Buildfile: build.xml

init:

javacc_check:

compile:
   [delete] Could not find file 
K:\projects\opensource\jakarta-lucene\jakarta-cvs\bin\src\org\apache\lucene\analysis\standard\
ParseException.java to delete.
    [javac] Warning: 
org\apache\lucene\analysis\standard\StandardTokenizer.java modified in 
the future.
    [javac] Warning: 
org\apache\lucene\analysis\standard\StandardTokenizerTokenManager.java 
modified in the future.
    [javac] Warning: 
org\apache\lucene\analysis\standard\TokenMgrError.java modified in the 
future.
    [javac] Warning: org\apache\lucene\analysis\standard\Token.java 
modified in the future.
    [javac] Warning: org\apache\lucene\analysis\standard\CharStream.java 
modified in the future.
    [javac] Warning: 
org\apache\lucene\analysis\standard\StandardTokenizerConstants.java 
modified in the future.
    [javac] Warning: org\apache\lucene\queryParser\QueryParser.java 
modified in the future.
    [javac] Warning: 
org\apache\lucene\queryParser\QueryParserTokenManager.java modified in 
the future.
    [javac] Warning: org\apache\lucene\queryParser\TokenMgrError.java 
modified in the future.
    [javac] Warning: org\apache\lucene\queryParser\ParseException.java 
modified in the future.
    [javac] Warning: org\apache\lucene\queryParser\Token.java modified 
in the future.
    [javac] Warning: org\apache\lucene\queryParser\ASCII_CharStream.java 
modified in the future.
    [javac] Warning: 
org\apache\lucene\queryParser\QueryParserConstants.java modified in the 
future.
    [javac] Modern compiler is not available - using classic compiler
    [javac] Compiling 102 source files to 
K:\projects\opensource\jakarta-lucene\jakarta-cvs\bin\classes

BUILD FAILED

K:\projects\opensource\jakarta-lucene\jakarta-cvs\build.xml:100: Cannot 
use classic compiler, as it is not available A common
solution is to set the environment variable JAVA_HOME to your jdk directory.

Total time: 3 seconds
================================================

I set the JAVA_HOME to where JDK is installed but that didn't have any 
effect. Running javac on command line works fine, meaning that I can 
compile java files without problems.

Does anyone have any suggestions?

Thanks.
Dmitry.