Trek'N Teresa,

Nice to meet another Trekker. I am by no means a pro, but I would suggest you concentrate more on keeping it clean and lubed. I don't think there is a hard and fast rule about replacing it but keeping it clean is another thing. Ride in the wet, clean & lube, ride in the dry and dusty, clean & lube. I highly suggest a good chain cleaning tool and from experience know that 1000's of miles is not unlikely if properly cared for! You probably saw at least a couple posts referring to "chain stretch" so measure it if you think it has stretched and replace it if it has. Don't worry about fixing what ain't broken, just clean & lube it!!