Oracle Database Discussions

I have a system running Windows XP x64 and Oracle 10.2.0.1.0 x64, which someone else set up. It has separate homes for the database, an ASM instance, and Oracle's Apache web server (x86 - not 64-bit). I'm needing to upgrade it to 11.1, and I'll switch to the embedded web server for simplicity.

When I run the universal installer, it fills in the Oracle base location as "C:\app\Administrator", which doesn't exist. I assume it will make administration difficult to have multiple oracle bases, or at least make removing the old versions of Oracle difficult when I can't find the folder. There's no environment variable set, and it doesn't appear to be reading the previous value from anywhere (a severe bug in the installer that it's not automatically stored and retrieved). I don't know how to find what is currently set up as the Oracle base. There are currently folders "C:\Program Files\Oracle" and "C:\Program Files (x86)\Oracle" that have inventory folders inside, a folder "C:\oracle" that has some of my files, and "c:\oracle\product\10.2.0" with 3 software installs and the admin folder. The only information I've found in the oracle documentation about finding the Oracle base location is "The Oracle base location is the location where Oracle Database binaries are stored." (http://download.oracle.com/docs/cd/E11857_01/em.111/e12255/oui2_manage_oracle_homes.htm)

I assume the documentation is wrong and the two folders that have inventory folders are my two current oracle bases. Is this correct, or should I look elsewhere?