Yes, use the --jdkhome <path> option when starting NetBeans. <path> is the root of the JDK installation.
The NetBeans installer looks for suitable JDK installations available on user's system and allows the user to select the one she wants to run NetBeans with. For the installer (6.0-M10) itself use --javahome <path>. However, the setting may become obsolete when the user installs a new JDK later, or may be inconvenient when she wants to run the IDE with another JDK. That's where the --jdkhome swich comes handy.
If you want to set the option permanently, you can do so in the netbeans.conf file.
netbeans.exe --jdkhome "C:\Program Files\jdk1.5.0_02"
netbeans --jdkhome /usr/bin/jdk1.5.0_02
Applies to NetBeans 3.6, 4.0, 4.1, 5.0, 5.5, 6.0
Platforms: All