Yep, your Windows 7 product key number will be able to install both the 32-bit or 64-bit version of your Windows 7 Ultimate. However, the installation disc is either 32-bit or 64-bit, so you will need to have the correct one you want to install as well. Of course, you can only have one installed at the same time and not both.
Actually, I find that using OPTION FOUR works the best, but it does a take a bit longer to do.
OPTION THREE is mostly only for if you get that error message.
Hope this helps,