To answer both questions:

Unfortunately, no; Nokia (or what's left of it) has withdrawn all support for the N900 and N9, including the sites to which those links were pointing.

That link gets you closer, but not quite there; the 1.2.1 version of the SDK has support for Harmattan (the N9's OS), but not for Maemo 5 (the N900's OS).

However, there is still a site containing a version of the SDK that will work with Maemo. (At least, it did when I tried it about three weeks ago.) If you go to this site:

ftp://ftp.informatik.hu-berlin.de/pu...l.no/QT/qtsdk/

and pull down version 1.1.2 of the "offline" installer (offline meaning that the installer contains the entire SDK; the "online" version just contains a link to the Nokia website), you can still get a working Qt SDK. (From my testing, I know that version 1.1.2 worked, and 1.1.4 didn't -- by 1.1.4, anything associated with "Maemo" had been removed from the SDK.) So for example, if you're using a 64 bit version of Linux, you'd want this package:

Qt_SDK_Lin64_offline_v1_1_2_en.run

After installing the SDK, there's still one more step needed: you'll have to run the SDK Maintenance Tool, go into the "Package Manager", and have it pull down the "Maemo Toolchain". (You'll find it under the "Development Tools" section.) Somehow, there is still a repository up and running that has the toolchain data.

(TMO'er xes found the link, and posted it in this thread.)