A.
Sysinternals provides the Contig utility, which you can use to defragment individual files or folders. You can download the tool here. To defragment a single file, use this format:
contig <filename>
To analyze the fragmentation status, add the -a switch, as this example shows:
D:\temp>contig -a en_system_center_capacity_planner_2006.iso
Alternatively, you can use wild cards in addition to the -s switch to search through the path given and any child folders and perform degragmentation on files matching the given file name criteria. The Config tool is a great utility to keep important files defragmented without having to worry about the entire disk.