Hello, I am starting my own gaming clan and I need a America's Army Theme, I looked all over the place for one but no luck, most of the ones I found are for e107.

Heres my website: http://skilledtofight.gamerhookup.com/

Converting a theme is not so difficult, but a lot of work.
Copy your existing theme to a working directory (from unknown-army to americas-army)
Download the other theme to your PC.
Check out the graphics and the place where they are used (eg block headers), CSS files may give away hints for this purpose.
Replace the existing images by graphics from the desired theme (may require renaming, splitting resizing, joining, ..)
Replace CSS instructions in the existing files with the ones from the desired theme (colors, sizes etc.)
There are a lot of tutorials about theming and CSS on the net.