This is usually due to a program that is reporting its installation information to windows improperly. This could be either a mistake in code or a milicious program (spyware). Suggest you run MS antispyware fully updated and a virus removal program. If nothing is found and you are having no major system problems/don't need to uninstall programs not showing in ad/remove programs,  I suggest that you ignore the gaps as they will just be cosmetic to you

Try downloading and installing Tweak XP
From what I remember this should give you access to the control panel and enable you to remove icons etc from the list that for whatever reason wern't automatically removed from an uninstall.

It might let you select the blank spaces and remove them!?

(also suggest running some form of anti-spyware such as Microsots Beta version - just to check that these gaps in the control panel aren't anything malicious sitting there trying to hide)

Good luck :)

Agree to CBCVF. You also can verify your uninstall list in
HKLM\SOFTWARE\MICROSOFT\WINDOWS\CURRENTVERSION\UNINSTALL
to see if the information is populated correctly.

Note that if you delete entries from the key HKLM\SOFTWARE\MICROSOFT\WINDOWS\CURRENTVERSION\UNINSTALL
, they will no longer appear on the Add/Remove programs list.  (Only if you know what you are doing)

You might also consider using a product like RegClean and see what it comes up with.

I believe you got AutoCAD software.  AutoCAD has fix on there website somewhere.  I really don't know where but if you search around you'll find it.  

This is usually due to improper installations or incorrect Video Drivers. Try updating your video drivers to the latest version.

If upgrading your Video Drivers doesn't do the trick, I also recomend probably uninstalling any software that you might think cuased the problem until you pin-point it. Like stated above, some software packs have problems reporting Windows, information about their installations properly (an example of this is how much space the installations some times occupy. I recall Ahead's Nero Burning Rom reporting 1.5GB installations to my clients sometimes).

Once you know what software is informing incorrectly, you can take a look at there website for any upgrades/patch ...

This isn't a Windows OS error.

This is alot of time due to the display icon entry in the registry.  You notice it most with AutoCAD installations.   For example, in the uninstall area of the registry (HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall) Autocad will have an entry for display icon listed like so:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{5783-F2D7-0065-049-0000-0060B0CE6BBA}
DisplayIcon
REG_SZ
C:\Program Files\AutoCAD LT 2000i\aclt.exe,-1

If you notice the -1 at the end, that is causing the problem. Negative numbers will cause the gap.

I can verify the accepted answer from smokenz420 as well as dufman's comment.

-It is AutoCAD
-The problem is in HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{5783-F2D7-0065-049-0000-0060B0CE6BBA}
  DisplayIcon
  REG_SZ
  C:\Program Files\AutoCAD LT 2000i\aclt.exe,-1
-Removing the ",-1" solves the problem.  Gap gone!  After all this time.
Thanks, Experts!
Tom Haws