If you have downloaded 64-bit Eclipse and a 64-bit JDK/JRE, check the availablity of javaw.exe for 64-bit.
In my case it was in C:\Program Files\Java\jre6\bin
I have extracted Eclipse to the c:\eclipse folder; within that the eclipse.ini file is available. Replace the contents of that file with the following:
-showsplash
org.eclipse.platform
--launcher.XXMaxPermSize
256M
-vm
C:\Program Files\Java\jre6\bin\javaw.exe
-framework
plugins\org.eclipse.osgi_3.4.3.R34x_v20081215-1030.jar
-vmargs
-Dosgi.requiredJavaVersion=1.5
-Xmx700m
-XX:MaxPermSize=690M
Leave the new line in between the -vm flag and the value. It worked for me.