First: Where is the oil leaking? From the side of the engine on top of the frame? Or, from underneath, above the double pulley?
Or, is it leaking around the trans-axle/ transmission area? Or, around the drain plug on the side of the engine, or the oil filter, if so equipped? Or, at the bottom of the dip-srick tube?
Give us some numbers for the type of engine, i.e. single or twin cylinder? Numbers will usually be on the tin flywheel surround part, stamped into the tin. Usually above the spark plug area. Or, on the valve cover.
When you tell us what area is showing leaking oil, then we can give specific instructions on what to fix.

also - if one didn't come with the unit - invest a few bucks in an owner's manual which will give you good info on adjustments, lube, operation,general maintanence, etc.
you can get one at:
http://techpubs.deere.com/deere/TechPubListing.aspx?EquipID=6206&Language=English
(cut/paste into yer web browser address bar)

make sure you have the unit's serial number to get the most correct manual...