Well, you asked several questions.
If your father is in dire straits, Adult Protective Services may file for the guardianship for free. You can contact them here: http://www.oregon.gov/DHS/spwpd/abuse/home.shtml
If there are other reasons, you can find a knowledgeable attorney through this organization: http://www.naela.org/ The money for the work will come from your father's estate.
Or, if you decide to do this yourself, your first step is to write up a Petition for Guardianship. Here is Oregon's website of free forms: http://courts.oregon.gov/OJD/selfhelp/index.page
Some courts may sell guardianship packets. I suggest that you call your county clerk's office, ask for the guardianship clerk, and then ask if they're available for purchase from their court or another.
After you figure out what to file in court (bring copies with you), you will need to properly serve your father with the papers. The easiest way to do this is to do use a legal messenger service. You can find them with a search online for Oregon.
The type of court you're looking for is "probate" court. It's not always listed, but it will be under state courts.
If you have any follow-up questions, don't hesitate to write back. There's no extra charge. I want to make sure your question is answered to your complete satisfaction.
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Thanks so much. I am taking a break now.