If you install 64. there is a few issues, applications like Office XP, that is a native 32, will not "see" the 64 Pervasive ODBC, vbscripts will not work either.
Pervasive 32 works very well.
To be quite honest, the 64/32 bit is a real pain in the butt.
I would install 64 only if all my workstations are Windows 7 and I have office 10