the modem is the one part of your current pc that is a pci card and you can move to the new pc. your sound, ethernet, and video (unless you’ve put in a new videocard already) are all integrated and cant be moved over. if you are planning on useing your same case measure it an make sure the new motherboard will fit.
the parts you can bring over will be your drives, cd dvd and or hard drive, modem, keyboard, mouse, ram (you have a 1 gig dimm) and if you have already bought a new graphics or soundcard those you can bring over, but nobody is going to buy a used pc stripped down that much. if you can sell it for more than it would cost you to buy the equilivant parts you can transfer to your new pc, just sell your pc and apply it tward the cost of the new pc, or even keep it as a backup incase you leave a loose connection on your new pc if you self build and need help figgureing out the problem. you could probably bring over the power supply too but it is so weak it would limit your new pc its only 300 watts which will really limit your choice of video card to probably an old budget card.
your hdd should be a 200 gig hdd, if its only showing 40 it has a problem so get a new hdd too. (unless you ment 40 gigs still free)
if you get an ati card get visiontek…most their cards have lifetime warrantees. it ever burns out you get a new one free. for nvidia cards i believe evga is a brand with lifetime warrantees and bfg is another.