I had a problem getting a connection to "SQL Server" on 64 bit PCs (running XP) even though 32 bit PCs connected easily.
Even compiling for 32bit was (initially) insufficient and to get it working at all on a 64bit PC, I ended up forcing its use of TCP/IP protocol by specifying a port number (that is apparently picked up as a default by 32 bit PCs once "SQL Server" has been added with it configured in "Control Panel --> Administrative Tools --> Databases(ODBC) --> Add --> SQL Server --> Client Configuration"
This worked for me on a 64bit PC, but only when compiled in 32bit: