It would be understandable to block pr0n or time-sapping sites (Facebook, MySpace, etc), but not professional resources such as these.
I strongly recommend that you book a 1-to-1 meeting with your manager and explain your case for requiring access to MSDN, Microsoft, *.se.com, etc and see what their response is. If, in a 1-to-1 meeting (i.e. private meeting room), they come out with 'I banned them to increase your productivity', you can:
- Ask how they are measuring productivity - by bug count, LOC written, or the number of times they spot MSDN open on your monitor?
- Point out that blocking these resources reduces productivity because you don't have reference materials, etc.
- Also point out that a move such as this has damaged yours/teams morale considerably and that the decision should be reversed.
Whatever you do, don't quit or go job-hunting without trying to work things out first. Describing your company/manager as a 'dinosaur' tells us that you may have some prejudices to address first and/or some gentle education of your management of modern software development techniques.