If I buy system builders copy of windows vista to put on a comp that i’m selling to somebody..what is the difference between this and the retail version? Can i use the retail verson on more than one computer? Or can i uset hte system builders copy for multiple? Is it illegal to use the retail on computers you are going to sell?

Retail you can use over and over again and OEM you can only use once I think.

There is always further reading about Niche Blueprint 2 here.