So here's the problem. I have to connect to both Oracle 8i and 11g databases. I have a 64-bit OS. Can I use the same 11g 64-bit client to connect to 8i? If this doesn't work, is there any other client that allows me to connect to 8i on my 64-bit OS? (on a previous 32-bit OS it was piece of cake to have the both clients installed). Thank you!
The 10.2.0 client is the latest client to support both 11g and 8.1.7. It shouldn't matter if it's 32 or 64 bit.
For more information look at the Client / Server / Interoperability Support Matrix For Different Oracle Versions (Doc ID 207303.1) on support.oracle.com. Unfortunately the document cannot be posted here, it can only be viewed with a valid support license. A valid support contract will also be needed to download 10g software since it's not on the public download page anymore. That bottom of that page mentions using Oracle Support Document 1071023.1 to request the software.