You can avoid using the queryChangedDiskAreas API on ESXi 3.5 based storage by parsing XML files for the namespace. For prepackaged methods that do this, see these SDK code samples:

Axis/java/com/vmware/samples/version/displaynewpropertieshost/DisplayNewPropertiesHostV25.java
Axis/java/com/vmware/samples/version/getvirtualdiskfiles/GetVirtualDiskFilesV25.java
DotNet/cs/DisplayNewProperties/DisplayNewPropertiesV25.cs
DotNet/cs/GetVirtualDiskFiles/GetVirtualDiskFilesV25.cs