Setting up a 32bit VB/Oracle app on a Win2008r2 64bit OS/Server can prove to be problematic.
Heres a link to my discussionfrom the Oracle OTN forum.
The key is using the windows 32 bit panel here c:\windows\sysWOW64\odbcad32.exe to create your connections using the Oracle 32 bit client/driver.
In addition theres a gotcha where you may have to configure, rather than add, an existing System DSN connection to get it to work.
Updated 8 May 2013:
ODBC connections can be very finnicky regarding white space. When creating a DSN make sure there is no whitespace at the end of the DSN Alias! It sounds stupid, and it is yes, but this can take a while to figure out 🙁