I'm just answering your questions about the RAM. As for the returning the RAM and getting new. That is your decision. Now.... Getting top of the line memory (Exp: Crucial Memory) isn't what you need unless your plan to overclock your computer. That isn't going to be likely because you are running a Dell, and the BIOS options are probally locked. Moving on..... If you do plan to buy more ram you will want to buy:

PC3200/DDR400 - Because the speed that is allowed on your computer is DDR400, so why clog it with slower memory.

2 sticks of RAM - If you want 256MB of RAM in your system buy 2 x 128MB sticks, or if you want 512MB of RAM in your system buy 2 x 256MB of RAM. This is because your computer runs in Dual Channel mode. This is so that your 800MHz FSB on your CPU will be equal to your FSB on your memory 2xDDR400=DDR800.

Recommend buying -
256MB Kit - http://www.newegg.com/app/ViewPro...20-141-421

512MB Kit- http://www.newegg.com/app/ViewPro...20-141-422

Also when after installing the memory make shure you get into the BIOS (Belive it either hitting the "Delete" key while the computer is booting up, or hitting the "F10" key while booting up) if you don't know how the Dell website will tell you how to. After getting into the BIOS make shure you enable Hyperthreading and Dual Channel DDR. I promise they will be in there.

Good Luck.