"all our righteous deeds are like a polluted garment" (RSV)Please don't be offended by the Douay-Rheims. It's the most literal translation. The Hebrew word `ed is used here to describe the rag; it literally refers to the blood from a woman's period. From this meaning is derived the sense of "filthy" or "polluted".
"all our good deeds are like polluted rags" (NAB)
"all our righteousnesses are as filthy rags" (KJV)
"all our justices as the rag of a menstruous woman" (DR)
Anyway, this verse is often taken out of context by non-Catholic Christians. They use it to show that our "good works" are displeasing to God. But from the context (Isaiah 64 at the very least) you can tell this isn't true. It was true for Israel at the time of this prophecy, but it isn't necessarily true of Christians today.