Followed the instructions here and here. I am using JDK 7u9 and NetBeans 7.2.1. What I did was create the whole path relative to my project
Found the answer here. It appears that the guidelines posted on the Oracle's website are currently mismatching the actual deployment scenarios available. Namely, when dealing with NetBeans, ant is unaware of the current directory that is presumed to be your root project. As it has been suggested in the according forum thread - simply add the directory containing "package/windows/${projectname}.ico" to ant's classpath and it will pick up the relevant resource, even though the tutorial claims that this should happen automatically due to the existing (?) addition of '.' to the build script.