I\'ve always been able to allocate 1400 megabytes for Java SE running on 32-bit Windows XP (Java 1.4, 1.5 and 1.6).
java -Xmx1400m ...
Toda
sun's JDK/JRE needs a contiguous amount of memory if you allocate a huge block.
The OS and initial apps tend to allocate bits and pieces during loading which fragments the available RAM. If a contiguous block is NOT available, the SUN JDK cannot use it. JRockit from Bea(acquired by Oracle) can allocate memory from pieces.