How do I make the JDK the default JRE?

The answer is "no," there is no way to get the JDK to be the default JVM upon install.

As the other answers point out, you can adjust your path and your JAVA_HOME to point to the JDK, or a different JVM entirely. This is in fact what the Java installation does in the first place.

However, your problem is that you want tools.jar to be found. To do this you can copy it to the ext directory under your default JVM. Check the JDK file structure here. This will probably work.

On the other hand, if modifying the JAVA_HOME and PATH variables for Java seems annoying, remember that it's just one of a series of things we do to keep us sharp

1. Download JDK from the website
2. Once everything is finished, go to Control Panel
3. Open JAVA
4. Click on the Java tab and select View
5. There will be one item present in the list. Change the Java Path from JRE to the JDK you downloaded, like so: C:\Program Files\Java\<your_jdk_version>\bin\java.exe.
   For example, mine looks like this: C:\Program Files\Java\jdk1.7.0_07\bin\java.exe