NSApplicationDelegate is a new protocol as of 10.6. You're getting the error (I'm guessing) because your application delegate is implementing this protocol. I'm not sure if this is the best practice on this, but you might just consider using the preprocessor to help you:
#if (MAC_OS_X_VERSION_MAX_ALLOWED <= MAC_OS_X_VERSION_10_5)
@interface MyAppDelegate : NSObject
#else
@interface MyAppDelegate : NSObject <NSApplicationDelegate>
#endif
I was finally able to accomplish this myself, but it took a little more work than I expected. Bochs can be a little temperamental to install, even on Linux.
Note
Forget about attempting to compile with Carbon. Apple is deprecating it and you won't be able to compile applications in 64-bit with it (the default for Mac OS X). http://appleinsider.com/articles/12/02/18/mountain_lion_focuses_on_cocoa_drops_x11_and_deprecates_carbon
BTW, the Bochs team doesn't use Mac OS X and probably won't be fixing this issue. This could be your chance to help an open source project: http://sourceforge.net/p/bochs/bugs/1204/
That said, you should be able to compile with SDL support with a little tweaking.
Install the SDL 1.2 Library
I could never get the SDL library from http://www.libsdl.org to work correctly, so I used Homebrew -- http://brew.sh -- to install it:
brew install sdl
Configure Bochs
I like to configure Bochs with the debugger (for OS development) and I like to install it into my home directory (in case I want to delete it). Here is the configure command I use:
./configure --enable-ne2000 \
--enable-all-optimizations \
--enable-cpu-level=6 \
--enable-x86-64 \
--enable-vmx=2 \
--enable-pci \
--enable-usb \
--enable-usb-ohci \
--enable-e1000 \
--enable-debugger \
--enable-disasm \
--disable-debugger-gui \
--with-sdl \
--prefix=$HOME/opt/bochs
Please note that I added --disable-debugger-gui because it is enabled by default if you choose to enable the debugger. However, since the debugger GUI relies on GTK+, and that isn't installed by default on Mac OS X, you want to disable it (GTK+ is another can of worms you don't want to deal with).
Building and Installing Bochs
Next, build and install
make
make install
Finally, just set your BXSHARE environment variable and update your path:
export BXSHARE="$HOME/opt/bochs/share/bochs"
export PATH="$PATH:$HOME/opt/bochs/bin"
Best Answer
The 10.5 sdk is not available for XCode 4.0. You will need to keep XCode 3.2.6 if you need it.