Once you install the 11gxe , you get the 4.0 installed by default.
Now, to cross check it , start ur database first.
Once the database is up, type this url in the browser
this is the default apex and it will take you to the adminidatration screen , you can create workspace and proceed further.
Incase you wanna upgrade it to the apex 4.1.
Download Zip file of apex4.1 and unzip it to c:\apex41\apex
Go to the command prompt , go to the C:apex41\apex\ and login to sql as sys as sysdba
username : sys as sysdba
password:- the password u gave for admin during installation of oracle db.
sqlplus>@apexins SYSAUX SYSAUX TEMP/i/;
this will update the schema of your database.
now acces the same url as mentioned above , go and create workspace and login to workspace and see the apex version installed :D