You can mount it as USB storage via recovery. Connect it to the PC, head to the mounts and storage menu in recovery and select mount USB storage and it should appear as a drive on your PC.
Ok, what you've linked to is an older version of Viper which isn't compatible with your firmware. With the official JB update, HTC altered the firmware so only certain ROMS work.
Here's the Viper you want to download: http://forum.xda-developers.com/showthread.php?t=2087443
Which recovery are you using? I'd recommend upgrading to a newer version such as TWRP: http://forum.xda-developers.com/showthread.php?t=1622925
Forget that teamandroid site btw, it doesn't look like it's been updated for a while.