Can I partition my portable 2.5 hard disk into 2 parts and then have one part as a Mac (ext journal) partition and the other as a NTFS filesystem?
You can use Disk Utility to partition your portable HDD into two separate partitions. You can then format one in the Mac format of your choosing. You can format the other as FAT, but you cannot format it as NTFS from within Disk Utility.
However, take the same disk to a Windows computer, mount the FAT partition, and the use whatever program Windows uses for reformatting (sorry, I haven't really used Windows much since Windows 3.1/MS DOS 6.2), and you have what you are looking for.