DSP is NOT the retail product but rather a more generic OEM version, if you will. DSP stands for "Delivery Service Partner" and was introduced by Microsoft's OEM Division many years ago at the request of smaller assemblers, aggregators and distributors so they could get access to Microsoft OEM-type licences for the machines they assemble. The whole idea was for DSP product to be bundled with new hardware (ie complete PCs) so the smaller distis could compete with the like of Compaq, HP, Dell and so on. It has been widely abused as the definition of a 'system' stretched to breaking point ... some distis have bundled DSP with components like mice & graphics cards or even RAM, which is in complete breach of the DSP agreement with Microsoft. These days DSP product does not include media, so you have to buy the media kit, which has all the main products on CD/DVD, allowing you to install on systems using the DSP licence codes. DSP product becomes part of the hardware and may not be unistalled and transferred to another PC, ie the licence lives and dies with the machine.
Microsoft FPP (Full Packaged Product) or Retail Product is the sstuff you buy in retail stores. it comes in a pretty pack box with media and quick start manual. The EULA for FPP is different from DSP - it can be transferred to a new system, for example.