64 or 32 postgres

How to figure out whether the installed postgres version is 32 bit or 64bit ? We installed postgres801 from src on susu box with EMT64 bit hardware. I assume since the hardware was 64 bit, postgres should have compiled in 64 bit too, but then we ran into this error

FATAL: database files are incompatible with server
DETAIL: The database cluster was initialized without HAVE_INT64_TIMESTAMP but the server was compiled with HAVE_INT64_TIMESTAMP.

HINT: It looks like you need to recompile or initdb.

Any ideas ?

Thanks,
Stalin