can I take darvocet and flexerill together?

Talk to your doctor or pharmacist before combining these two drugs as they can be potentially dangerous when mixed.  Darvocet is a central nervous system depressant and flexeril is a muscle relaxer.  Among other things, when combined they can cause respiratory depression.  And definitely avoid alcohol when using one or both of these medications.  Also, you should not eat grapefruit or drink grapefruit juice when taking flexeril. 

A good site for checking potential drug interactions is IQ Health's Drug Information Site.  You can enter the medications you are taking or considering taking and it will give you any potential interactions.