Actually, there is no need at all to wipe the disk using dd for the task you want to accomplish, it will be nothing more than a waste of time and stress for the hardware.
Just proceed with your installations.
For the sake of completeness, the correct command to wipe the disk would be
dd if=/dev/zero of=/dev/sda bs=8M
You can play with the blocksize to get better performance, the size which gives the best performance depends on your hardware.