MSVC6 is the tool for you. Use it exactly same way like debugging of windows binaries. A tip, click F5, breakpoint F9 [menu / debug] :-)
Symbian binaries are common dll files on the emulator environment. Everything what you can do with windows dll you can do for your application dll (.app)
EDLL.LIB(UP_DLL.obj) : warning LNK4099: PDB "edll.pdb" was not found with "\Symbian\7.0s\S80_DP2_0_SDK\EPOC32\RELEASE\WINS\UDEB\EDLL.LIB" or at "C:\Symbian\7.0s\S80_DP2_0_SDK\EPOC32\RELEASE\WINS\UDEB\Z\SYSTEM\APPS\EXAMPLE3D\edll.pdb"; linking object
as if no debug info
Is it normal? Could you please tell me how to display debug string (on debug window)?