Should be, you would be better off building a Computer yourself or have a friend help you build one then these branded computers they sell to people with no computer knowledge or know how.
I am not sure if your PSU can handle it but how about something like the HD5670 or HD5770/HD6770. that would be pretty cheap, most PSU's "should" be able to handle it and it would run WOW pretty well as well as other games and 3d applications.
If I were you just to be on the safe side I would get a better Power Supply Like 500W or 600W and then put a card like the GTS450 or GTX460. Not that anything is wrong with the HD5770 and a 300W PSU, Its just that these cheap OEM low wattage PSU's dont have much headroom and a bad PSU can bring more problems then good. So If I were you I would Upgrade the PSU and the Graphics Card. If it a Regular ATX PSU/Case you can probably get it done yourself in less then half an hour. Dont worry about anything else, PCI-Express x16 is enough for most high end PCI-Express 2.0 and mid end PCI-Express 3.0 cards. and its not like you would mind a few frames here and there, the boost you will get from any mid range card would do you fine in WOW and most other games.
.Edited by TheBirdman74 - 7/22/13 at 8:35pm