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I would recommend a quad core mac pro with a 30" cinema display and 16 gig of RAM. It will help no end when she is doing inverse kinematics and particle system replication.
 
I would suggest the new iMacs. even with the 20" model the screen is big enough for her to see things nicely. The lowest price one with 1 gb of RAM is pleanty fast enough for most tasks. It is easy to setup and Easy enough to move around.
Depening on what you have available Mac Mini may not be the best price. If you need to get a keyboard mouse and display a Mac Mini could end up costing more then an iMac and have more of a hassle.
 
If she has a digital camera, 80GB may fill up fast especially if that camera can record videos, such as Casio EX-S series in MPEG4 format so that it does not fill up too much space on the card (half an hour on 1GB card at its highest quality, it looks OK on TV.) Of course, the flip side is you end up recording quite a bit of movie clips on trips, birthday parties and what not, so you end up filling up your hard disk in the end. Still, 80GB is not that small, either.

60 is not that much of an age barrier to get into iPhoto slideshows and clips onto DVDs. Besides she will need some kind of backup mechanism. Never trust a hard disk with your memories. Once you include SuperDrive, Mac mini is not a very good deal unless you already have a nice monitor.
 
OMG. If you would of posted this earlier. Just last week, I was on the Colorware PC website and the iMacs (last generation) were $500 and they were brand new and you could even get it a different color. I swear they were on sale because they needed to get rid of them because they are going to start selling the new iMacs not the old ones. I would of been a great deal! I'm so sorry but try going to the website and find a number and call them and ask them if they still have some. Who knows maybe they do. The website is www.colorwarepc.com
 
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