the Map32bit installer will prevent that the program is installed on a 64bit OS. I don't know if there is a technical reason for this but "out of the box" you will not be able to install und run Map 32bit on a 64bit OS.
In the past people hacked the installer to get a 32bit piece of ADSK software installed on a 64bit system. Search in all Autodesk discussion groups for further information on this.
Another - quite unelegant and probaly more costly workaorund is to use a 32bit virtual machine on top of your 64bit host OS.
Still "DEVELOPING" 32-bit-only AutoCAD application? It sounds not making sense, considering AutoCAD 64 bit being available since 2007(Acad2008) and now being 2012 (acad2013). How does the appplication work with AutoCAD 2008? I'd imagine it is most likely the application isdeveloped with MS .NET (since it works with AutoCAD, there little choicce not to use anything else other than .NET). If so, the application most likely can work with both acad 32bit and 64bit, unless the application has to use some 32-bit third party code/component...Even so, since the development is still developing, it makes more sense to get it to work with 64-bit Acad than to try to stay with 32-bit AutoCAD with latest OS and AutoCAD.