I'm having some difficulties of my own. I'm running Windows 7 RC x64 with WMDC 6.1.6965.
I started by running the sspl.bat (with USB enabled in WMDC); the SPL app came up on my device's screen, I tapped ok, and the device screen went black w/ solid black pixels. The only way of rebooting it is yanking the battery. The OS loads fine after that.
Later I thought it had run sucessfully so I ran auto.bat. The JumpSPL steps ran fine (with USB enabled still) but it failed at step 4 when the ROM tried to flash (obv. because USB was still enabled).
Strange thing is, when USB is disabled and I run auto.bat, the device is unable to connect in steps 1-3. I canceled all those steps and then the ROM flasher starts, makes a connection, and starts the flash but won't go past 0%. The screen is still black because after step 3 the SPL flashes (or attempts to.)
I later put the device in bootloader manually (with the colorful bars) and ran the ROM flasher by itself. It runs but again, gets stuck at 0% on both the device and the PC. After a while a 262: update error pops up. This must be because the SPL is still locked? The OS boots fine after a battery pull.
Strange. Any advice would be welcome.
Anyways, if you run auto.bat, disable USB Connections after the screen turns black via ActiveSync. In your device manager (with the screen still black) look at your USB Devices. You should see a entry called HTC USB Sync. If you see that continue to flash. Seeing HTC USB Sync is a key step in this whole process.
Please read the testing/development thread for some good solid help. A bunch of us ran into the same issue you did. If you read all 4 pages you should be able to troubleshoot your problem: http://forum.xda-developers.com/showthread.php?t=550628