1) The oem package will have a oem key inside.
2) All windows-7 dvd's are exactly the same, either 32 bit or 64 bit. The key you use to activate is what determines how you install, and what version of windows is installed.
In your case, if you can borrow a 64 bit windows dvd, you can use it to reinstall, using the original key that was given to you. See if you can't download a legitimate ISO so that you have a dvd to use. A dvd has some repair and recovery features that you may find useful.
The oem package you bought will serve this purpose, but you will have a extra activation key that will be unused.