Hi sharkhunter and welcome to the Q&A Board!
I don't use Arcshot software, though I have it. I find the crop tool difficult to use and there is little in the help files about it.
Free programs such as Irfanview (
www.irfanview.com) and Picasa
www.picasa.com let you adjust the aspect ratio so you can crop to standard sizes such as 4x6, 6x4, 5x7, etc. Give them a try and see if they work for you. Remember to work on copies or originals, and not an original image file.
If you have more questions, please let us know.
Related reading - apsect ratio
http://www.digicamhelp.com/what-is-aspect-ratio/what-is-aspect-ratio.htm