ok so i've been doing some research on bmw DSP. i know what DSP is, in general, but what exactly does having DSP in your bmw mean?

if you have an x5 without dsp (2005, navigation) then what do you need to buy to get it, approx how much and what level of difficulty to install?

from what i've been reading (altho it wasn't for x5's with navi) it's possible

THANKS!