Limit Dwarf Fortress processor usage

You can, in theory, limit the game update speed and/or graphic update speed, DF will try to run as many updates as possible with respect to the limit, your CPU is stuck at 100% because it's not fast enough (don't worry, as far as I know there are no CPUs fast enough to run DF at the default speed without using all the CPU).

Although settings this at even, say 1, might not work (depends on how the limit is implemented, it should say to the OS "I don't need to do anything for X milliseconds" but it's probably a low priority bug) it's worth a try.

If you have a dual core processer (or higher) you could try opening task manager, clicking the processes tab, locate the process for the game, right click and then select 'Set Affinity'. Once the new tab is open you can choose how many cores that process will use at any one time - limiting it to 1 might help with your problem as part of the processor will no longer be in use.