First off, save yourself heart ache by buying pre-finished flooring for your DIY project. Sanding and finishing is a science best left for the pros.
As far as tools, just make sure you have ALL the right ones before you begin....Too much time is spent screwing around if you don't have the right tools. 400 square feet on your first flooring project will take you at least 2 weekends so renting all this stuff may cost you more than if you were to just buy them.
Here are the power tools you will need:
Compressor (most will work fine, Costco is a good place to look)
Flooring nailer/stapler (staples actually hold better according to many here)
I have laid over 1000 square feet with this
http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=93197 and it works awesome!
Table saw & a Miter saw. You will need a Table saw to rip long peices of wood. There are other ways but make it easy on yourself. Again, Costco has a unit for $79.00.
15 guage finish nailer for the first and last rows.
18 guage brad nailer to nail the base boards on to the wall.
(Schucks Auto Supply has a 3 pack (15 guage/18 guage/Fine Wire) that I use with great success $129.00 for all 3.
Read as much information on this site as it will be VERY helpful.
Good Luck!!!