Let's say you have one actual hard disk drive on your computer. You can "cut it up" into as many pieces as you want to make "other" drives besides the C drive. In your case, it looks like you only have one other drive, which is D. Ignore the name DataPart, it is meaningless, it's just another place to store things on your computer and acts as a separate drive.
The numbered folders have letters and numbers which are often referred to as GUIDs - globally unique identifiers - and are generated by the operating system or anti-virus software when quarantining a virus or infection. For the most part, if you don't know what they are for, or what is in them, leave them alone. There are times where the operating system may also put Restore Points (system backups) into those folders depending on how your computer is configured.
If things are running slow, there are other steps you can take, such as un-installing any programs that you don't need or don't want running on your computer. The other is to disable any Windows Services that you don't need, but this is more difficult of the two and should be approached with caution.
If you're looking to free space on your D: drive, you should search for files that are over a certain size and see if they are any that you recognize first before deleting them.
Hope this helps!
edit on 24-6-2012 by SonOfTheLawOfOne because: (no reason given)