Ram or Harddrive?

Im going out tommorrow and buying a radeon 9550 and 330 watt antec powersupply for my Athalon 1800+ computer. I currently have 384 pc2100 ram and a 40gb 5400 rpm hd. first of all will i see a noticable difference if all i upgrade is my Geoforce mx440 to a radeon 9550? secondly, i can buy either a faster hard drive, or a stick of 256 or 512 ram to replace a stick of 128 i have. would i see a bigger preformance boost with more ram or a hard drive that wont slow me down? also, if the ram is preferable, how much preformance would i get more if i replaced a 128 with a 256?

World or Warcraft will be taking up most of my time at first. I played it with my mx440 and it works fine, just could look a little nicer. I just dont want my hard drive slowing me down at all. I play call of duty and UT2004 demo quite a bit. I used to also play halo frequently. I would get a radeon 9600 but i hvae to shop at Compusa for this specific purchase (long story) and the difference in price between the 9550 and 9600 is significant. Also, im going to be replacing a 128mb ram stick with a 256 or 512, how will it look differnt than my 256 stick? I'm fairly new to upgrading my computer myself and dont want to screw anything up.