Current version of osrmt doesn't suport installing on 64bit systems. To solve:
1) Download the latest izpack.jar file
2) Extract the native/ShellLink_x64.dll and rename to ShellLink.dll
3) Overwrite the existing osrmt.jar/native/ShellLink.dll with this new one. (FWIW, I also copied COIOSHelper.dll into that directory, not sure if it's required)
Presto, a 64-bit installer.
I cannot find a /native/ folder in the download for Version 1.5. Does this version fix a 64-bit install? I am getting just a flash of the Command Monitor (Windows) menu and then there is no opening of the OSRMT client. Also, the install does not add an icon for OSRMT anywhere that I can find. All I see is the OSRMT folder in the Start menu and it gives the behavior mentioned above when I left click on OSRMT Client.