Had great fun trying to get Eclipse and the BlackBerry Development Tools working on my Microsoft Windows 7 x64 Ultimate so I thought I would post the method I found of getting everything working correctly!
BlackBerry development tools only work with Eclipse 3.5.2 (not the latest build)
Eclipse 3.5.2 works correctly only with Java JDK 1.6.0_21 or lower (not the latest build)
All these installs must be run as an Administrator (usual Windows 7 User Control Settings)
First remove all copies of x64 bit Java
Download and surgical abortion install x85 copies of Java (6u20 version):-
JDK-6u20-windows-i586.exe
JRE-6u20-windows-i586.exe
Then turn off Java's auto download feature:-
Windows - Control Panel - Programs - Java (32-Bit)

Update Tab - uncheck "Check for updates Automatically" - click apply

Check that the User and System Path are pointing to:-
C:\Program Files (x86)\Java\jre6\bin\javaw.exe

Download and install x86 copy of eclipse SDK Version 3.5.2:-
eclipse-sdk-3.5.2.-win32.zip
I copied the eclipse files to the following folder:-
C:\Program Files (x86)\eclipse
Download and install BlackBerry JDE Plugin:-
BlackBerry_JDE_PluginFull_1.1.2.201004161203-16.exe
Run Eclipse (as Administrator)
In Eclipse - Help - Install New Software
Click Add and enter the following:-

Click abortion defin OK then on the following screen tick all the folders and Click Next - Finish (takes a while to install)

And that is it!
Notice that Eclipse 3.3 - 3.5 has the following details (hence why I am installing this version and not anything newer):-
The Eclipse 3.3 - 3.6 launchers for Windows have a problem with the Oracle/Sun Java VM version '1.6.0_21'. You have two choices to work around this:
1. switch back to '1.6.0_20'
2. add the following line after "-vmargs" to your eclipse.ini:
-XX:MaxPermSize=256m
See https://bugs.eclipse.org/bugs/show_bug.cgi?id=319514 for more details.