depending on which state you're in, you may need an attorney or closing / escrow company to help with the transaction basically you negotiate the price directly with the owner get a blank residential purchase contract, fill in and sign by both parties. don't forget the contingencies give your deposit money to attorney/escrow company get an inspection, ask for necessary repairs or renegotiate the price get the loan schedule for closing
for your case, it will be fine without a agent for the transaction. but strongly suggest that you hire a real estate attorney to help you. not that you are going to get into trouble, but you need someone who not only knows about the process, but also can protect you in case something bad happens. you never know what will happen and better be safe than sorry.