To simulate RGBA and HSLA background in IE, you can use a gradient filter, with the same start and end color (alpha channel is the first pair in the value of HEX)
background: rgba(255, 255, 255, 0.3); /* browsers */
filter: progid:DXImageTransform.Microsoft.gradient(GradientType=0,startColorstr="#4cffffff", endColorstr="#4cffffff"); /* IE */