use C++. The version of the SDK depends on your targeted phone device. For Symbian OS 6.1 you could use 1.X only, and for OS 7.0 best would be 2.X SDKs, thou 1.X applications works if are very careful when doing them.
hmm, not really sure what you are asking. But the Software Development Kits (SDK) basically need Integrated Development Environment (IDE) , before they are anything usable.
Currently there are 3 IDEs, MS VC6/NET, Borland Builders and Metrowerks Codewarrior. So depending on which IDE you use, you also need to select SDK that supports the selected IDE.
Anyway See Metrowerks, or Borlands WWW-pages, for information of evaluation versions of their IDEs.