You can find the OpenVMS Hobbyist program here: http://www.openvms.org/pages.php?page=Hobbyist
. They require you to be a member of a user group, so you'll have to search around a bit. You can now download the required images, which is a real help as you used to have to buy the CD for $30. When you register, they'll send you a couple emails with license pak numbers for VMS and the associated layered products. You'll have to use these to get everything running. It's a pretty fiddly process--but there's an excellent follow-along tutorial by Phillip Wherry, available here: http://kuhl-us.com/gadgets/retrocomputing/vax-simh.html
. It's from 2004, but everything's still the same. (VAX/VMS hasn't changed in that time as far as I know--the last available version is 7.3.)
You'll have to have some form of alternative (larger) storage available to do this, since the VMS disk images are far larger than the storage available on the SD card image. I used a USB hard disk that I had laying about, the original drive from my 2007 Macbook. The trick is getting the root filesystem onto the drive so it can take over and leave the SD card behind completely once the kernel boots. To do this, I used VirtualBox on my Mac, running Ubuntu 12.04, to mount the second partition of the 04-19 Debian image as a read-only filesystem using a loopback. I then connected the drive to the Pi, initialized it with a new set of partitions (using 'parted') and formatted the large 110Gb partition as ext4 and the small 8Gb partition as swap. I mounted the large partition, then used 'rsync' to copy the root filesystem over from the virtual machine on the Mac to the mounted partition on the Pi. Once it was done, I edited the etc/fstab file so it would activate the swap partition on reboot, and then edited the command line parameters in the SD card so that the root parameter pointed to /dev/sda1 (the large partition on the USB drive), and rebooted. The Pi came up and did its normal first-time initialization, and it's been running fine ever since. It's much, much faster at disk operations, of course... the SD card is slooooooooow.