I have a Windows 7 Professional DVD, but it doesn't specify whether it is 32-bit or 64-bit.
If it was a 32-bit DVD, can I use it to also install Windows on a 64-bit system, or do I need to get another copy of Windows which is 64-bit enabled?
You just need to delete a file in the image and it will unlock all the versions with 32 and 64 bit selections.
Both say "(includes 32 & 64-bit versions)".
Don't know if other answer is old editions, but those two copies seem to have both on one DVD. Which is my understanding of what comes on the DVD.
I also have a DVD for my work computer which specifies 32bit. Since it's a 32bit computer, they may have built a copy just for it (Dell included DVD).
Moral of the story: It probably depends on your DVD. I'm fairly certain that customer DVD's include both versions.