Best Intel Desktop deal?

I am contemplating a switch to Mac from Windows,and have seen a number of sub $550 Intel 1.5 Mac Minis, on Ebay.Is there some reason not to buy one of these units? I simply surf the web,email some pictures,and do some word processing.Is the $999 Imac a better deal? Any coupon or refurbs available for a discount? Thanks for any help.
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I set up a Mac Mini for an older lady at work and it is a great little machine. It works great for her, but all she does is sync with her iPod, surf the net, and check e-mail with a little Office 2004 work every once in a while.