Dual boot is possible. you can dual boot windows 7 by making a separate empty partition and choosing it to install win7. They work well in dual boot . However you may have some issues regarding the Drive letters in both OS i.e the partiton hierarchy on Hdd .
Yes, pirated ones are installed and work successfully . No doubts abt that

.Well if you want to remove Vista Home , just boot via Windows 7 DVD and open the installer and it will show you a list of your partitions and let you choose. Choose C:\ where vista resides and format it using the installer and choose it to install windows7 .