I've read through some of the threads here, but my head's spinning with all the aftermarket talk. I want a 21" iMac to replace my aging 2007 MBP but I really want a dual standard-HD/SSD set up. Can I order a 21" with both set up? Or can I after-market install an SSD into the 21", in addition to a regular HD? How hard is the latter and how much would I save? Thanks in advance!