Installation
First of all, sign up for an Oracle Web Account: http://www.oracle.com/admin/account/index.html
Now download and install JDeveloper 10g: http://www.oracle.com/technology/products/jdev/index.html
Once you've followed all installation instructions, it may ask you to install updates. The update manager will need your Oracle Web Account email address and password at some point.
If you are not prompted to install updates, you can do so later by selecting Check for Updates from the Help menu.