?? question ??

First thing is that GParted doesn't merge partitions. Furthermore, in your case (partition with software installed) I think it is impossible or at least risky to proceed to any automatic partition merge, if any program is able to perform. There are lots of references to the various files in both the system registry and configuration files, that it is rather impossible to update.

Second, it is possible to modify the size of the partitions, to shrink the second partition and grow the system partition. To do so, you have to:
- Shrink the partition that contains D: by moving the start point to the right.
- Shrink the eventual extended partition, in case there is one (this configuration it is quite usual). This is necessary in order to have the unallocated disk space directly after the partition we need to expand.
- Expand the partition containing C: , by moving the end point to the right, to take the unallocated space. You have to leave the "Round to cylinder" box unchecked, otherwise the entire partition could move, and make the system unbootable.

After resifing an NTFS partition, you need to boot the computer into windows, at least 2 times. Then, the system will run the chkdsk command. If it doesn't make it automatically on the reboot process, you can do it yourself from the command line window (chkdsk /f) . Although it is possible to schedule big number of operations in GParted, I would recommend to proceed step by step, so that you check if the system is behaving as expected after each operation.

You need the GParted livecd (actual stable version 0.4.6-1). It contains everything is needed to boot and work. Before proceeding, you need to run the defrag tool from windows 1-2 times. This can be a problem for the overloaded partition, as defrag usually needs at least 15% free space to work. In this case, you can try to temporarily move some big files from the partition elsewhere and/or deactivate the virtual memory file, empty recycle bin, temporary internet files, to make free space as possible.

Take backup of any important files. Most of the times there is no problem, but if a problem occurs it could be fatal for the data. Professionals prefer to take double backups.

Read carefully the documentation page. GParted is a powerful program and there is no undo for many critical operations. In general, it is not recommended at all to stop a started operation.
In case of doubt, you can always post here a screenshot from the GParted screen, to ask advice.

(Moved to the Live Media section)