I have to respectfully disagree with my esteemed colleague, Steve D.
"Correcting" what he said, a PSD that was made w/o proper intention or knowledge of web design will surely make a mess of things. This however is less the fault of the PSD graphics than the LACK OF FORESIGHT by designer and client.
Once a WELL THOUGHT OUT design is constructed, the technical of slicing CAN BE (tho not always) as simple as SLICE FROM GUIDES and SAVE TO WEB.
After that of course you can will use the HTML/CSS you planed the design around to just import the images as element BGs, pseudo elements, etc.