Buy the laptop with as little RAM as possible then upgrade it with RAM you buy from ANYONE ELSE besides the company that made the laptop. When I ordered my Dell laptop it was $300 for a 128MB stick but only $150 if I bought it somewhere else. That is quite a difference. Just make sure that the laptop uses standard memory like 144 pin SODIMM and you will be all set.
As for the hard drive, laptop hard drives are very expensive and don't seem to advance very quickly in technology. I would suggest getting the 10GB to tide you over for a while until hard drive prices drop and you can get more storage space for your dollar.