yes, dude , 512 MB = Vista on life support

its very less resources for running vista (esp in aero mode )
like sukhdeepsinghkohli just said ,its a memory hogger ...uses up all the RAM it gets..but having said that ,let me also add that vista is running exactly like its supposed to.If u add another 2 GB RAM, vista will use that up too..the logic behind this is that un utilized RAM is wasted RAM. so it utilizes fully the available RAM.But if u launch another ram hungry app, more memory is allocated to that.
To cut a long story short,upgrading your RAM might not mean u will find RAM utilization at lesser levels ,but it does mean u will get a better and faster vista .