There is no oil
filter in a two stroke. Your bike has two types of oil for the engine.
In the gearbox, it uses a light viscosity 2 stroke motorcycle gearbox oil.
Then you have the oil that you pre-mix with your fuel(to lubricate the top-end & crankshaft bearings).
Oil for your bike is best purchased from a motorcycle shop- this is a racing bike that requires race type maintainance.
The better the maintainance the longer it will last.
Keep the chain lubricated.
Keep the air filter clean & oiled correctly with propper air filter oil(this is REALLY important).
Use high octaine fuel-(if in Australia like me-no ethanol fuel- 98 octaine).
Use the best quality 2 stroke oil you can afford-preferably full-synthetic.
Here is a link to parts fishes(exploded diagrams) for your bike.
These will help you see all the parts & gives a good idea on what goes where.Click on the part name & it will show you a picture. : )http://www.mrcycles.com/fiche_select2.asp?category=Motorcycles&make=Honda&year=2003&fveh=3243
If you have any other questions don't hesitate to ask.
Kind regards Andrew Porrelli