If you are getting the "java is not recognized as an internal or external command" then you did not install Java correctly. Try this:
a) Got to
http://www.oracle.com/technetwork/java/javase/downloads/index.html, scroll down to the "Java SE 6 Update 27" section and click on the JDK Download button in that section.
b) On the downloads page, click the "jdk-6u27-windows-i586.exe" link (unless you downloaded the 64-bit version of Eclipse, in which case
you should choose " jdk-6u27-windows-x64.exe")
c) Once the exe file is on your PC, run it and follow the installation instructions. (By the way, by default it will want to install in C:\Program Files; I usually change that to install at c:\apps\java. Having spaces in paths sometimes causes problems for Java apps.)
After that is done, try running the "java -version" command again. You should get some output identifying the version. Then try running eclipse again.
If you still get the "java is not recognized as an internal or external command" error after doing the above steps, at a command prompt enter "set path" and post the results (most likely your PATH is messed up)