Just to step through a few of the biggest problem areas:
Complete doctype and character encoding like this:
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<TITLE>PowerOverWireless.com - Home</TITLE>
You can only use an id once. That first one could be renamed #header maybe.
The second #wrapper needs the floats cleared.
<DIV id=headercolumn1><A href="http://www.poweroverwireless.com/"><IMG height=65
alt="Power Over Wireless" src="power_files/logos7.png" width=564 border=0></A>
I usually use a strict doctype that requires you to close things.
I THINK that html 4.01 lets you do it this way, but I'm not sure... I'm used to adding a </li> to close each list item.
<LI><A tabIndex=1 href="http://www.poweroverwireless.com/">Home</A>
<LI><A tabIndex=2 href="http://www.poweroverwireless.com/power.html">Power</A>
When you resize the site narrow enough, the content in each column breaks out the bottom. Need to figure out how you want to handle that, overflow: auto; maybe?
There is so much stuff in #resourcebox that I lost count of the divs!
I think there was one that was not closed though? Check the validator for that.
To get a box around your 3 columns at the bottom just have #resourcebox enclose #resourceheader and #resourcecolumn1 through 3.