Narrowing It Down A Little Bit More
First, @Brian -- thanks, bud. I appreciate your kind words.
Second, I've done a little more testing with Comodo Internet Security (CIS).
In version 3.11.108364.552_XP_Vista_x32, no adjustments or disabling of any kind that I tried within Comodo and within its Defense+ mechanism (including using the option to permanently disable Defense+ and restarting) made any difference. With this version, on my machine, Comodo Internet Security simply breaks CSS Sculptor's preview functionality. I suspect that in some way CIS is hardwired to be too aggressive.
I found the setup file for version 3.9.76924.507_XP_Vista_x32 online, and installed that. Hmm, preview worked with that version installed. However, when I let it update itself, then preview broke.
So this narrows the problem down to a "mystery" change that took place in CIS somewhere between version 3.9.76924.507_XP_Vista_x32 and version 3.11.108364.552_XP_Vista_x32.
I was hoping that the problem was somehow core to whatever version of CIS was originally installed and that updates would not break Sculptor, but I should have known better, as that was exactly what my history was (albeit when I wasn't paying so close attention).
At the moment, I've switched to AVG 8.5 Free for anti-virus and plain ol' Windows Firewall. CSS Sculptor works fine with those two in place. I may try another free firewall out there to get a little better protection, maybe the ZoneAlarm or some such. I haven't tried installing Comodo Firewall as a standalone from the CIS installer, so maybe I'll check that out and have a little more info to share here later this weekend.
I believe that that is all the news that's fit to print!