The "Answer" to this question is adequate: however, here is a processes that worked for me.
I was very sketchy about entering the OS name into the "Boot File Name" prompt.
So for comfort's sake, here it is if you guys need it.
After getting to the "Hit any key to run loader" prompt the first time, I aded the boot version's name, and IP info etc... and copied the software to the on-board flash disk. (note, these are partial clippings, not everything, just what's relevant to this post.)
Boot File Name [screenos_image]: Loadssg5ssg20v133.d
Loaded Successfully! (size = 408,395 bytes)
Image authenticated!
Save to on-board flash disk? (y/[n]/m) Yes!
Saving system image to on-board flash disk...
Done! (size = 408,395 bytes)
Run downloaded system image? ([y]/n) Yes!
After running the software, the ssg5 was stuck in the boot loop you were talking about.
After getting to the "Hit any key to run loader" prompt again I entered the software name "ssg5ssg20.6.3.0r12.0" (without quotes) in the boot file section.
Boot File Name [Loadssg5ssg20v133.d]: ssg5ssg20.6.3.0r12.0
Save to on-board flash disk? (y/[n]/m) Yes!
Saving system image to on-board flash disk...
Done! (size = 13,353,346 bytes)
Run downloaded system image? ([y]/n) Yes!
this began loading the system image, once that was done it booted as follows: (please wait for it to finish.)
The previously installed version was SSG5 Boot Loader Version 1.3.2, and Version 6.2.0r5.0. The system is usable.
After completing all steps, the system booted with: "Juniper Networks SSG5 Boot Loader Version 1.3.3", and Juniper SSG5/SSG20 System Software Version 6.3.0r12.0.
After getting to the login prompt I rebooted the device using the reset command. Once this was complete I powercycled the unit using the power cable. (It came back up successfully without a software loop.)
(The system hardware used was a Juniper SSG-5-SB, an SSG5 with 128 MB Memory, and RS232 Serial backup interface.)
All software was downloaded from the juniper web site downloads section. ( http://www.juniper.net/support/products/screenos/ssg5/6.3/#sw )