just use the mds simulator from 4.1 but develop using the 4.2.1 jde...
if you develop using the latest jde be aware that you'll break compatibility with older devices.
i wouldn't switch to another jde until you are a little more experienced developing blackberry applications (give it a couple of months until it feels comfortable and routine and you know the framework, then look into using eclipse or netbeans).
new job doesn't allow a public profile - please do not contact this user with questions, you will not get a response. good luck!