I have a 256GB Samsung SSD on my laptop and there are 2 primary partitions (oem and os) as well as 1 logical partition (recovery). I have about 22 GB of free unallocated disk space at the end of all these partitions. However while installing Debian or any other Linux distribution for that matter, after creating one partition (eg /boot) it does not allow me to create any other partitions, and says that the remaining disk space is "unusable". Here is a screenshot of Windows Disk Management :
http://s7.postimage.org/h4zom7ty3/diskmanager.png

What could be the problem and how do I fix it? Thanks.

PS If I install Linux and Grub on my external HDD, would I still be able to boot without connecting my external drive at boot time?

You have to create extended with locals within it. With debian you can choose "Use contiguous Free Space" "Guide Partitioning" & let it setup additional partitions.

Simple solution is don't create a /boot partition. Use just one partition (22 Gig) for the complete install - no (separate) /boot, no /home.
Use "expert" mode on the partitioning in need.

Pretty ugly, but your choices are limited due to the lame layout you've been lumbered with.

Edit: @EDDY1, the OP already has an extended - for that logical. Like I said, lame ...

If I choose guided partitioning, it will still let me dual boot right?

Doesn't Linux require different partitions like swap for hibernation etc? What other problems would I run into if I install everything on one partition? And I still don't understand why it. says unusable space!

Oops ... forgot about swap ...

As it happens, Linux will run without swap, but you probably don't want to go there.

Any partition you create will be the fourth. At which point you are rooted re using any other space. This is not a Linux restriction, but a hangover from MSDOS. Blame M$oft.

In these sort of situations I just delete the lot, and re-install Windoze, then create a large extended, and use logicals as I see fit.
I find the OEM and recovery partitions useless - presumes you have (real) Windoze CDs/DVD; vendors seem averse to providing them these days.

UGH!! Did it come installed that way?

Honestly i would reisntall the whole thing making reasonable partitioning, and also with Linux alone on it, because it would need way less room for the system / leaving a lot more room for /home, plus with SSD the speed... it would FLY !!

Here Ubuntu on an 80GB disk you can see the usage is minimal:
Now win7 just the OS will take about 20GB with all updates.


Regards

Alright, so I thought that there was a limit of 4 primary partitions but it seems as if there is a limit of 4 partitions in general. That sucks.

Yeah lol Dell shipped it that way. I do have the original Windows 7 DVD that came with it but not at the moment. I am kind of hesitant about deleting the OEM partition since that contains all the diagnostic tools. I don't know what the recovery partition is holding at the moment though. Maybe I could just delete that?

From the look of the diskmanager screenshot, you have the OEM partition, a logical partition, then the windows partition (an odd arrangement, that).

So, use either such tools as windows provides for partition management, or gparted from a liveCD, as follows:

1) drag the right hand end of the windows partition to the right to take up the free space.

2) drag the left hand end of the windows partition to the right to resize windows partition to the original size.

That will, in effect move the free space to the left.

3) extend the logical partition to the right to take up the free space.

4) make your Linux and swap partitions inside that logical partition.

Nope - you were correct the first time. That logical exists within a special primary partition called an "extended partition" (a container for logical partitions). More than one logical can be created if space exists within the extended. That is what @bigrigdriver is trying to explain.
However;
- it is the extended, not the existing logical that needs to be enlarged in 3)
- all new partitions must be then created as logicals, not just swap. This is not an issue for Linux, but may be for some distro installers in default partition layout.
- I didn't suggest this as I've never been successful in moving the (main) Windoze partition. Usually needs some registry hacks. Hence I find a clean-out and re-install better. Linux is (infintely) more flexible and accommodating in being moved around.

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^Thanks a lot! That really helped clear up some of the questions I had!
I'll try to work something out now.

OK one more question : if I use partition wizard to move the beginning of my OS partition to the right, as suggested above, would it cause any problems?

In my personal, biased opinion, one should never, never, NEVER, go mucking about with partition boundaries without first making backups of affected partitions onto separate storage media, such as cd, dvd, or another hard drive.

Failure to follow this advice could leave you, in biblical terms, wailing, gnashing your teeth, and uttering numerous mea culpas.

With gparted-live-cd you can just drag(move) the whole partition to the right, but you have to put mouse in the center of the partition.
It will also show where the free space actually is.
Can you post the output of