Hey,
I rode an '87 XR200 up until this last year. I ran automotive type oil in it for a couple years, and never had any problems. However, I have found that the Pro Honda GN4 and HP4 oils are some of the best you can use.
XR's use the same oil to lubricate the transmission and the motor. Automotive oil is fine for your motor, but it's worthless in your tranny. The "4-stroke" motorcycle oil you see around, including the GN4 and HP4, have additives for lubricating the tranny. By the way, I use 10W40.
Xrsforever was correct when he said to change your oil often. Your aircooled motor, and tranny will get very hot when you ride. This heat quickly breaks down the oil. So yes, change your oil after every couple rides, and keep your airfilter clean just as often. Not as often, but just as important, is keeping your valves and cam chain adjusted properly. Your little 200 will run forever if you properly maintain it. Go to your local Honda shop and get a Honda Service Manual, they are about $60, but well worth it if you care about your bike. Good luck, and keep on thumpin'!