Ok so i built a new computer but im taking the hard drive from my emachine et1331g which has windows vista 64bit on it
what i need to know is do i have to wipe the hard drive to instal windows 7 on it?
No you don't have to.
or can i just switch everything up and when its all
wired together can i just pop in the windows 7 disk on boot up and it will un-install windows 7 vista?
they ONLY thing im taking from my emachine is the HD
During the Windows 7 install you'll have the option to select the partition where to install, and provides a tool for deleting existing partitions.
In this case, I suggest that delete all partitions, and select the resulting free space as the target for installation. (You need to click on "Advanced", while in the tool.) The installer will do the rest.
Please realize that the answer selected will erase all data on the HD.. Hope you dont have anything important on it.
My reply can be shortened like this: "No, you don't have to wipe the drive, the installer will do it for you."
What I didn't add, but also worth mentioning, would sound like this: "No, you don't have to wipe the drive, if you don't want to. If you do an upgrade instead of a clean install, your existing files will be moved into a folder named Windows.old."
But if you have important files on the disk, I can only repeat what lafontma wrote. Back them up on another medium, and after that, you can do it either way.