I have Rhapsody installed and the QNX 6.4.1 evaluation version (Neutrino/Momentics). I have been trying to code generate, and have attempted to follow the instructions (on p161 of the Frameworks and Operating Systems Reference document) for rebuilding for the QNX framework.
When I attempt to 'make', I get the following response:

C:\Program Files\IBM\Rational\Rhapsody\7.5\Share\LangCpp>make -f qnxcwbuild.mak CPU=x86 PATH_SEP=\\
make all -C oxf -f QNXCWoxf.mak CFG=oxf
make[1]: Entering directory `C:/Program Files/IBM/Rational/Rhapsody/7.5/Share/LangCpp/oxf'
C:/QNX641/host/win32/x86\usr\ntox86\bin\ar -rvu QNXCWoxfx86.a QNXOS.o os.o IOxfEventSender.o omreactive.o omthread.o OMEvent.o OMTimeout.o OMNotifier.
o omstring.o OMDelay.o OMTimerManagerDefaults.o OMTimerManager.o OMOSEventGenerationParams.o omprotected.o OXFURefManager.o OXFRefManager.o OMDefaultI
nBound.o OMDefaultOutBound.o OMDefaultReactivePort.o OMDefaultMulticastOutBound.o OMDefaultMulticastReactivePort.o OMDefaultMulticastInBound.o OMMainT
hread.o oxf.o OMHandleCloser.o OMThreadManager.o OMMemoryManagerSwitchHelper.o ommemorymanager.o OMMemoryManagerWrapper.o OMMemoryManagerSwitchHelperI
mpl.o state.o OMAnimReactive.o OMAnimHelper.o OXFTimeManagement.o OXFDllGuards.o OXFEvents.o OXFTypeSafeContainers.o
process_begin: CreateProcess(NULL, C:/QNX641/host/win32/x86\usr\ntox86\bin\ar -rvu QNXCWoxfx86.a QNXOS.o os.o IOxfEventSender.o omreactive.o omthread.
o OMEvent.o OMTimeout.o OMNotifier.o omstring.o OMDelay.o OMTimerManagerDefaults.o OMTimerManager.o OMOSEventGenerationParams.o omprotected.o OXFURefM
anager.o OXFRefManager.o OMDefaultInBound.o OMDefaultOutBound.o OMDefaultReactivePort.o OMDefaultMulticastOutBound.o OMDefaultMulticastReactivePort.o
OMDefaultMulticastInBound.o OMMainThread.o oxf.o OMHandleCloser.o OMThreadManager.o OMMemoryManagerSwitchHelper.o ommemorymanager.o OMMemoryManagerWra
pper.o OMMemoryManagerSwitchHelperImpl.o state.o OMAnimReactive.o OMAnimHelper.o OXFTimeManagement.o OXFDllGuards.o OXFEvents.o OXFTypeSafeContainers.
o, ...) failed.
make (e=3): The system cannot find the path specified.
make[1]: *** [QNXCWoxfx86.a] Error 3
make[1]: Leaving directory `C:/Program Files/IBM/Rational/Rhapsody/7.5/Share/LangCpp/oxf'
make: *** [oxflibs] Error 2

Any suggestions as to the problem, and more importantly, what I should be doing?

So simply unzip this on top of your share and edit sitec++.prp file accordingly. (see example file)

Let me know if you're struggling.

Also, you should install the Rhapsody Workflow into Eclipse to allow you to utilise Momentics features more easily. There are 4 Rhp/Eclipse items available: Platform, Platform in WorkBench, Workflow and Workflow in Workbench. Add <rhpInstall>\Eclipse as a local site to your eclipse (Momentics) install and you should see the options. The 3rd is the only one worth using IMO.

Once you've done that then you can simply right-click on a configuration in Rhp and Change To Eclipse Configuration. Watch as it magically creates a project in Momentics. Use Empty C++ project. You can then right click on both sides to see 'Locate in Eclipse' and 'Locate in Rhapsody'. You can change code and it'll round-trip (advise that you set the CPP Roundtrip option for your configuration to Advanced rather than Respect or Basic though).

Of course you can do all of this with standard Eclipse + CDT (Ganymede), Cygwin and Rhp 7.5. It's not just available for QNX or Windriver Workbench. It's fantastic as you get code level debugging etc for free. You could alternatively use .NET 2008 with Rhp 7.5 to achieve the same effect.