If there is nothing in the slot underneath the PCI-E x16 slot on your motherboard(or nothing you can't move) then it shouldn't be a problem. The better question is whether or not your power supply can handle the new card.
Is the a reason you want that GTX 550 Ti in particular? It isn't a very good deal for the price.
There is another slot, and beneath it is says PCI2, and my power supply can handle it, also is there a better card than the 550 ti for around $150?