The Symbian S60 Toolchain isn't available for Linux, it's Windows only. I downloaded the Windows installer for Qt Creator and just ran it under Wine. The install went mostly fine, except 'simulator.exe -registeronly' failed, and now the IDE shows and works OK, but when I try to compile for S60, I get:
:-1: error: [release-gcce] Error 2 (File not found)
Update
I tried something else. Some files were missing from the Wine installation, so I copied the entire QtSDK directory from a Windows install. Now the compilation produces a .sis file which can be installed on my phone, but when I try to run the application it won't start. It shows the busy cursor equivalent in Symbian for some time, but then terminates before actually showing a window. On the other hand, .sis files created with the same QtSDK from the Windows machine install and run fine.