This is an old thread, but I'm sure many guys still suffer the dual Oracle client installation.
I managed to install both R2 versions of the Oracle Client without one installation messing the "client1" groups on the start menu and registry keys created by the other installation.
The trick is edit the oraparam.ini file found in your installation files at winXX_11gR2_client\client\install\. There all you need to edit is the key DEFAULT_HOME_NAME. Note the installer will weirdly add a "1" at the end, whatever you put there, so that's why I left the underscore at the end of each. This is how I left mine:
For 64 bit install:
For 32 bit install:
After the installation this will create two folders at the Start menu:
Oracle - Ora11Home64_1
Oracle - Ora11Home32_1
And in the registry you'll end with:
HKLM / Software / Oracle / KEY_Ora11Home64_1
HKLM / Software / Wow6432Node / Oracle / KEY_Ora11Home32_1
When you create ODBC or similar objects you'll get then the proper naming referring if it's using the 32 or the 64 bit driver.
Supposedly you can feed the ORACLE_HOME name trough the command line parameters when running setup.exe, but got sick of trying to find the way to make it work and the installer never liking it so editing the INI just makes the trick.
BTW - If anyone is going trough the dual install I highly recommend downloading the separate uninstaller so you can get rid of everything easily without going trough that annoying installer.