anything is better then you got now.
but to get a decent card you need atleast a 450W PSU, bare minimum 350W.
without a good one, your pretty stuck.
you could get a 550W Cooler Master PSU
for 50$ and then get a HD5770
with that PSU, and that Card, you'd easly be able to play FSX or any other game max on your monitor. Yes it is very over kill for your size screen, but its a good future proof product.