We are running an AS400 v5r2 and I have iSeries Client access installed. Since v5r2 does not support a x64 ODBC driver does anyone know how I can either install two versions (v5r4 supports x64) of iSeries Client Access on the same box or just install the x64 odbc driver from the more recent version without uninstalling all of v5r2 components.
Installing two versions of Client Access is probably not going to work, since both register their ODBC drivers with the same name, so only one would be available at a given time.
OTOH the PC side of V5R4 Client Access would probably work without problem with a V5R2 OS/400; perhaps even 6.1 iSeries Access, too. So you can upgrade the x64 box and check whether everything is working. FYI, I had problems with the first versions of 6.1 iSeries Access when running on x64 boxes, later versions were a bit better; also, I do not remember that V5R4 Client Access had a 64-bit variant at all.
Do not forget that on a x64 PC, there are two different ODBC drivers, one for 32-bit applications (stored on C:\WINDOWS\SysWOW64\cwbodbc.dll and that you can manage with the 32-bit administradorC:\WINDOWS\SysWOW64\odbcad32.exe), and another one for 64-bit applications (stored on C:\WINDOWS\System32\cwbodbc.dll and that you can manage with the 64-bit administrador C:\WINDOWS\System32\odbcad32.exe.) Unless your application is recompiled for 64-bit, what you are interested in is the former one, and if V5R2 Client Access runs flawlessly on that PC, everything is fine. Some applications like Office 2010 come in two flavours, but precisely for compatibility reasons like ODBC, it is still recommended to run the 32-bit variant even on 64-bit workstations.