Testing Service packs & security updates

Create a small test environment (not separate from your production network) with all your critical applications.
Install service packs and updates in the test environment and run your critical apps through their paces. Be aware that unless you conduct exhaustive (and time consuming) testing, there is no guarantee you catch any glitches. While time might be a luxury you can afford with service packs/normal program patches, it usually is not a luxury you can afford when it comes to security updates. While you are testing, your systems remain vulnerable .

Although it's best implemented from the get-go, VMware can be a real time/headache saver... but ultimately I agree with Tim Walsh...