So I did all that and then it says
Should I continue or will this not allow me to have Windows 8 on there?
You should not have run into that error following the instructions in that article. Extend the volume back to what it was before and start over.
If you only have one HDD, you are shrinking C (you should probably give w8 at least 32-64gb) by however much space you want to give W8. Then you right click that unallocated space you subtracted from C and click New Simple Volume.