I am a windows user only because of my work and I just got married. I am looking at getting a new iMac and was wondering whether to get the 17" or 20" iMac. I use Autocad. I am currently using a 17" crt at home and a 19" crt at work. The 17" is way too small for me, and the 19" almost works. The iMac will be my new home machine and was wondering if anyone knew the actual square measurement of the 17" and the 20" iMacs screen, and which one to buy? Also should I get Applecare?