I am using the rgba opacity code in the .content rule so the background color is transparent, but the other elements (text and images) are not affected:
.content {
padding: 50px 0px;
width: 70%;
float: left;
background-color: rgba(0,0,0,0.5);

But having a conflict with IE: the background color simply doesn't show.
Suggestions?

IE sees the background-color:rgba(0,0,0,0.5) and doesn't know what it means, so it throws it away altogether, treating it like background:none.

You have to use -pie-background:rgba(0,0,0,0.5) so that PIE can see the value and use it.

so the css code is now:

.content {
padding: 50px 0px;
width: 70%;
float: left;
-pie-background:rgba(0,0,0,0.5);
}

correct? or just:

.content {
padding: 50px 0px;
width: 70%;
float: left;
background:rgba(0,0,0,0.5);
}

You'll want both actually. And to be safe, you could provide a fallback for other browsers that might not recognize rgba:

awesome. although not tested everywhere, it looks like it's working. my hat to you!