FreeBSD 4.8 and FreeBSD 5.x lower version of 5.x difference

[bridgett hamilton]

I need to know the difference between FreeBSD 4.8 and
FreeBSD 5.x lower version of 5.x difference. I am
acquiring Verisign as my Ecommerce who only has an SDK
for 5.x. Need to know the difference between 4.8 and
5.0 so I know whether or not I am going to run into
problems. Also can you tell me if we upgrade to 5.0
will there be any lost of configuration or data?
Please advise. Thank you. 

Bridgett