Windows 7 - Hard Disk Logical partition is safe to delete?

HI im just new here, I want to ask someone who can help me out with regards to hard disk partitioning, I have a 500gb seagate HDD and its my first time to do partitioning thru the help from the net.I managed to do a partition and name it as B: Backup files used 60gb set as primary.my C:which installed a windows 7 on it uses 114gb of 254gb and i created another one E: as vista 151gb of 152gb which currently empty. I intend to install a vista here on E: but it is currently set to logical drive.Is it safe to delete this drive?when i try deleting it i had this prompt message: THIS IS AN EXTENDED PARTITION,THE PARTITION WILL BE INACCESSIBLE IF YOU DELETE IT.ARE YOU SURE YOU WANT TO DELETE IT? what's gonna happen if i continue to it??I want to creat a dual boot using a single HDD.i want to start again and create a new partition as primary partition. Please help!

The reason you get this message is the limitation of 4 primary partitions per volume. The extended partition allows you to create many more partitions. If, however, you create 4 primary partitions, you are stuck with that maximum of 4.
You can delete this extended partition, just make sure you do not paint yourself into a corner creating 4 primaries (unless 4 is all you want).