Well the first thing is that the Motherboard does have a PCI-E x16 slot, so thats a good start
The bad news is that it only has a 300 Watt Power supply, so you will be very limited what card you can put
A GTX460 1GB which costs around £130 is a very good card for anything upto a 24" screen..the problem you may have is that the Vostro case looks quite small and these cards are often a foot long (12")
The GTX 460 1GB at idle uses around 140 Watts and at load 270 Watts
If I were you, you can either get a lesser GPU, or buy a new case and bigger PSU aswell as the GPU
It all depends how long you want the 'upgrade' to last :)
You can get a lower powered GPU that will fit for now, maybe even last 2 years (but at some point not long after that your going to need to start changing tp a bigger case, more watts etc anyway)