The easiest thing to do is download the sample PIP script which you can download from here:

http://hotkeynet.com/wow/wow-pip.html

After you download it, if you want to substitute a different size or location for your little window, here's how you plug in the numbers:

Code:
<Command SetPip>
<TargetWin %2%>
<SetWinSize WIDTH HEIGHT>
<SetWinPos X_POSITION Y_POSITION>
<TargetWin %1%>
<SetWinPos 0 0>
<SetWinSize 1680 1020>
<TargetWin %2%>
<SetForegroundWin>
<UpdateWin>
<TargetWin %1%>
<SetWinRegion X_POSITION Y_POSITION WIDTH HEIGHT>
<SetForegroundWin>