SWT on Windows 64-bit
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!
I faced the same problems a couple of weeks ago. We develop an RCP application that must use 32bit SWT, but we work on 64bit machines.
What we had to do was to change Eclipse's configurations so it pointed to a 32bit JVM. We did it on Window -> Preferences -> Java -> Installed JRE's. On this preference page, we changed all references from "Program Files" to "Program Files (x86)".
I hope it helps you somehow.