Software Version Control

Problems occur when software is not upgraded to acceptable versions. The software may no longer be supported by the vendor, putting us at risk. Other times, we have one piece of software not upgraded that causes a ripple-effect for other software remaining at back levels. This causes us to maintain support for too many versions and results in us being slow to adopt newer technologies. We need to have a policy for when upgrades should be done. We also need to understand the political and financial impacts for those policies. Has anybody been through this before and come up with a solid software version policy?

Thanks,
Ed