I have a HD5450 at the moment and its great for watching blu-rays and some light gaming.
I take it that the educational games aren't very demanding?
The good points of the HD5450 are:
1) very cheap card
2) You won't need a new power supply
3) their silent, passive cooling
4) Plenty powerful enough for streaming films/light gaming
1) The PC case will need good cooling as the graphics card doesn't have any active cooling.http://www.overclockers.co.uk/showproduct.php?prodid=GX-046-HS&groupid=701&catid=56&subcat=1711