Did you remove the JDK that was installed on your system or did you remove the one that MyEclipse may have been referring to? You can either specify a new one by editing your shortcut and adding a -vm argument (pointing at the javaw.exe file you want to run MyEclipse with) or you can reinstall a default system JDK by going to Sun and downloading the most recent stable JDK release (I believe it’s 1.5.0_09)