How to install Oracle 10g Express and 11g Enterprise on same machine
It appears that you don't need to worry too much.

Install XE first.  You don't get to choose the database name (XE) or the port (1521).
Next, install 11g to the default app folder.
Modify the TNSNAMES.ora files for both databases so they know about each other.  Test connections and create database links and you are good to go.