That makes perfect sense
Thank you! 
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Thank you! 
as your friend just wants desktops and not eyefinity gaming, just get the normal 5450 and a HDMI to DVI adaptor/cable
each of the 3 screens will still be able to have different things on each screen and not just mirrored (which is what he wants)
Won't work, even in extended/mirror mode the third screen must be from a Displayport output.
To OP, looking around it seems they're pretty rare now. What motherboard does your friend have? It may be better to get two cheap cards instead. It will still give what your friend wants, each screen displaying different information.
the cheapest DP card i can find is;
http://www.overclockers.co.uk/showproduct.php?prodid=GX-163-MS&groupid=701&catid=56&subcat=1866
Would I be able to do it with a Zotac GTS 450?
1 x DVI-I (dual link) - 29 pin combined DVI ¦ 1 x DisplayPort - 20 pin DisplayPort ¦ 1 x HDMI ¦ 1 x VGA - 15 pin HD D-Sub (HD-15) ( with adapter )
The only thing is it says Mini HDMI..