I have an external hard drive and I want to partition it into 2 partitions which are EXT4 and NTFS.
Is that OK with this kind of partitioning and is there a problem with partitioning an external hard drive rather than internal one?
This should be very easy depending on which tool you are using to format it with Ext4 and NTFS. I would recommend using a GPartEd Live CD. I know of many people who have a dual boot system with one being a Linux system such as Ubuntu 10.10 with a file system of Ext4 and the Windows 7 obviously having an NTFS file system. Weather the drive is internal or external has no relevance to the file system being used. You may use any file system you want.
=Good Luck