FreeBSD download

[bernardos at cits.br]

Dear Sir or Madam, 
 
I'm interested in using FreeBSD as part of rearrengement of my professional skills. 
I'm currently studing Linux but I'd like to feel a bit of a true UNIX system. 
 
I noticed FreeBSD is presented in a 4 CD set case by FreeBSD Mall, for example. 
However, the download options are different. 
I supose the minimum I might download is: 
   4.8-RELEASE-i386-disk1.iso (610.4MB) 
   4.8-RELEASE-i386-disk2.iso (259.1MB) 
 
What is in fact the other 2 files? I.e.: 
  4.8-RELEASE-i386-mini.iso (199.6MB) and  
  CHECKSUM.MD5 (203 bytes) 
 
Do I need them too? 
 
What shall be the 5.x release? What is the "new technology" you will include in it? 
I might probably buy it (a combo promotion of 4 CD set + Handbook 2nd edition). 
However I'd like to know a bit more about it first. 
 
Could you send me more information in order to clarify my doubts, please? 
Thanks in advance for your assistance. 
 
Kind regards, 
Bernardo 
+55 41 9911-2666