Extended partition normal?

I recently upgraded to a larger 320GB* HDD for my M1530. Initially, there were no partitions.

1. Created 200GB NTFS partition for Vista during the OEM Vista install. The remaining space was unpartitioned. Vista installed fine (C: ).
2. Created 30GB NTFS partition for XP during XP retail install. For the remaining space, I had two entries of unpartitioned space, one for 90GB and one for 8MB which I thought was a bit odd. XP installed fine (E: ).
3. Repaired Startup Recovery using the Vista OEM DVD. Installed EasyBCD once in Vista so I could dual boot.
4. In Vista and XP, I noticed Disk Management first displays the Vista partition. Then, it displays the XP partition and the 90GB Free Space together as an extended partition (surrounded by a dark green border). Vista Disk Management goes further and displays the 8MB unallocated space after the extended partition (while XP Disk Management does not).

Why is it being considered as an extended partition? Is this extended partitioning normal?

* GB/MB sizes aren't exact but rounded for simplicity.

 

More or less normal. For a discussion of the differences between a primary partition and an extended partition, see this Wikipedia article.

Basically, a hdd can have only 4 primary partitions or, if you want more root-level divisions, can have three primaries and one extended partition, which itself can contain up to 23 logical partitions.

In terms of moving the stub unallocated space around so it can be useful, I would suggest using Acronis Disk Director or a similar partition management app to get better control over the partitioning of your drives - the MS functionality is competent, but not very sophisticated.