Is it possible to load older versions of Autocad on the Vista platform. Currently there are error messages that say not compatible with 64 bit.

32-bit versions of AutoCAD are not compatible with the 64-bit versions of operating system (independently of OS version - XP/Vista/7). Use the 64-bit version of AutoCAD (available since AutoCAD 2008).
 
Windows 7 officially supports AutoCAD 2010 (and later). You can use the WinXP Mode of Win7 to run older AutoCAD versions.