Your system has a PCIe connector and a 350w PSU so the GTS 450 card will work.
But so will many other cards. Whether or not it is the "right" card depends on how you want to use it, your budget, and the resolution of the monitor you use. Provide more information and perhaps we can be more helpful.
Note that the GTS 450 is primarily a multimedia card and not a gaming card. For more information, see this review:
If considering gaming applications, a good place to start a search for good cards is the THG article on the best video cards for the money, updated monthly to reflect new prices and new cards. Note that it includes links a very brief description of the performance level of the card plus links to reviews with detailed performance benchmarks, most often with comparisons to other cards:
and just calculate your cost using exchange rate. That should easily narrow it down to a card or two - with some good information about the cards, include links to reviews so you can see the performance.
Alternatively, post a link to an online site you might use so we can see the prices you are looking at.