We're down to our last 4 rows of hardwood...the nailer wont allow us to get close enough to nail them down.

How do we get the last 4 rows set?

3.25 oak .75 thick

If you have a 15 gauge pneumatic finish nailer, use that to blind nail the next two rows and top nail the last two. If you do not have a finish nailer, then you will need to pre-drill and hand nail using # 8 finish nails, available at any hardware store. Using an electric drill, chuck a finish nail into as a bit and drill through the togue of the flooring at 45 degrees every 8" and within 2" of the ends. Simply hand nail the boards being careful not to damage the wood. Use a nail set to counter sink the nail heads a little. Last rows will need to be nailed through the top (or face). Select a grainy part near the tongue side to nail into. If your subflooring is 5/8", try to locate and nail into the floor joists and in between. Use a matching colored putty to fill the nail holes.

I prefer 6# casing nails for toe nailing. That way you don't have to drill.

I concur with Gary as to nailing at the joists. Even if you don't penetrate them, it is the easiest and most firm place to drive a nail.

I mentioned nailing at the joists locations because there are so many different subfloors and underlayment systems out there. It wouldn't be necessary with a 3/4" plywood suybfloor and a 1/2" plywood underlayment, or a myriad of other, thicker wood subfloor and underlayments. But the 5/8" subflooring over joists 16" oc is the MINIMUM NOFMA accepts and for hand nailing, it is better to attempt to tag the joists, especially when face nailing. Since a #6 is 2" and a #8 is 2.25", both will go into the joist when driving them straight down. And hold better in the short and long term. As far as which nails are best, true flooring nails or cut nails hold the best but can be difficult to find. Casing's greater diameter will most definitely allow for driving without drilling but one does risk splitting near end butts. When making recommendations, I always consider who I'm speaking to. In this case, a novice DIYer. Sending him on a journey looking spiral shanked flooring nails would probably result in failure so I took the simplest route.