I don't understand the previous reply so if you don't understand it either, let it go on by. That is not a valid reason to avoid Google Analytics in my opinion. I do understand others disagree with me on this, so make your own decision.
Google Analytics is for tracking website visitors, visitor flow, content visited how many times, and more like this.
Prosper202 is for tracking advertisement displays and can handle things such as affiliate tracking and conversion tracking (this overlaps with Google Adwords, which also does a type of conversion tracking) - this answers the question "where did this conversion come from". I see in your post OP you say Google Analytics can do this too, but the difference is prosper202 can tell you specifically "who" sent you a conversion. I don't think Google Analytics can do this.
Running prosper202 is akin to running your own affiliate network, and I believe the software is designed to do just that, specifically handle affiliate oriented statistics tracking.
If someone disagrees with me about this, please post your point. I am open to, and I welcome, suggestions, improvements, and tweaks to my understanding.