All righty...the package arrived today. First off, Stealth, you're the utter master of packaging materials; it took me a good twenty minutes to get through all that.

(Woo bubble wrap!

) Unfortunately, as Klaustrophobia surmised, the power supply you sent doesn't fit in my case...not only is it a bit longer than the spring-clip mount can handle, but the actual plug input would be covered by the case's sheet metal. That aside, I successfully installed the new card, and it seems to be running properly, at least for the moment. The fan's pointed straight downward sort of halfway into my wireless card, which makes me wonder how the airflow will work out, but there isn't much I can do about that anyway. I haven't given the system a real graphical workout yet (MV_Advanced hooo!), but if I start experiencing instability, I'm guessing the PS would be to blame, and I'll take the next step of looking into a new case.
Again, Stealth, you're the man.

(Strangely enough, my case didn't come with any screws for securing cards laterally, so I have a slightly-too-small one stuck through the hole to hopefully provide some extra stability. The plus is that it probably won't wobble as much, since I no longer have to use the DVI-to-VGA adapter with the direct VGA port.)