Linux Mint 15 Lockup?

Definitely get a PCI-Express 2.0 card
Lots of them out there, but 3.0 is the new kid on the block

depending on your budget, a GeForce GTX 650 is pretty nice...

PCI-Express 2.0 cards:
$124 GTX 550 Ti$250 GTX 560 Ti

PCI-Express 3.0 cards:
$109 GTX 650
$150 GTX 650 Ti

There is no guarantee these will work on your board because they are 3.0

What kind of MSI board do you have again?

Avoid 3.0 cards unless you have a 3.0 motherboard; not all 3.0 cards will work in 2.0 slots.

Exactly, I had a friend learn that the hard way. he had to take the card back.

A heart break in the making....