I would not recommend a diy job - it is not your carpet and you will not be insured if the carpet shrinks, discolours or has some other damage as a result of the cleaning.
Not all carpets can be cleaned by home cleaners. This from the Rug Doctor site:
Before you begin, you should know that Rug Doctor machines and cleaning products are safe for most carpets. HOWEVER, you risk damage to carpets not intended for water extraction method cleaning. DO NOT use the Rug Doctor machine or cleaning products on: Natural fibre oriental rugs (silk or wool), hand-loomed wool rugs, braided rugs, sisal or jute carpets, silk, Haitian cotton, brushed corduroy, leather or non-colourfast fabrics. Some stains require professional treatment.