This is a great question that I tend to see a lot. There is the ServiceNow Wiki Article that many people point to, but the complications that most people have with it is that the information given there is for technology that many organizations have outgrown, such as Microsoft SCOM 2007. ServiceNow has since discontinued supporting new SCOM connectors, so the best option for most companies is to either buy a connector from a third party, or custom build their own SCOM connector.
Our company sells a connector called ConduIT that is specifically built for ServiceNow customers, and has pre-built packages for both SCOM and SCCM, among others. This solution is fully supported meaning you don't have to maintain custom code. Building your own connector is not impossible, but it also isn't easy with constantly changing technologies, which your company most likely has. Let me know if you have any questions on our connector, though, and I'll be happy to help however possible.
