On 64-bit JVM’s you need the 64-bit SWT. Current versions can be downloaded here:
http://archive.eclipse.org/eclipse/downloads/drops/R-3.6.1-201009090800/index.php#SWT
Note the first two downloads, the first is for x32, the other for x64.
Note: Even on 64bit Windows, if you use the 32bit JVM, you still need the 32bit SWT version!