Well it is most likely that you can upgrade to 2GB when ordering the laptop, yes it would be costing more, but the 2x512MB sticks wouldn't have been bought and the money wasted.
What you need to look at the minimum specification for the version of Vista you want to run and if you are going to rum aero glass then video ram if shared would be a factor as that would be coming off the 2x512 sticks, further reducing what you have left. By all accounts 2GB is almost the minimum if you want to run other applications with many reporting 4GB being the ideal.
I think Vista is a rip-off period, it certainly is in the UK where it costs roughly twice the US price. It will be some considerable time before (if I ever do) I get Vista.