Floor boards
Added on the February 7th, 2007 update.
Creation
21xPlank
2xLarge Nails
Activate a Plank, right click on Large Nails and click Create->Miscellaneous->Floor Boards.
Activate a Plank, right click on Floor boards and click Continue. Repeat 21 times.
Activate a Large Nails, right click on Floor boards, and click Continue.
Then, activate the Floor Boards, right click a Packed Dirt tile (however, unpacked dirt will work as well), and select pave.
The floor boards, before planting, will always say they are birchwood, whatever wood you have used.