You will be ok with that power supply, unless you order a bad one. Stick with brands like Antec, seasonic, etc...
Also make sure you get the GDDR3 version of that video card not the DDR2 one.
Are you sure you have AGP on your system or a PCIe slot? I did not think that the 775 socket had any motherboards with AGP.
It's an AGP slot. Also, I will be buying this case that comes with PSU. Is it OK? http://www.ebay.com/itm/Frisby-ATX
Also, why should I stick with GDDR3? Is there a problem with GDDR2? Also I have the MSI 848P MoBo