WoW mimimum requirements:
# Intel Pentium III or AMD Athlon 800 Mhz or higher CPU
# 512 Megabytes (MB) or more of RAM
# 32MB 3D Graphics card with Hardware Transform and Lighting (such as an Nvidia GeForce 2 class or better)
# 6 Gigabytes or more of available hard drive space
# 4x CD-ROM drive
# DirectXョ 9.0c (included with game) and latest video card drivers
Recommended requirements:
# Intel Pentium IV 1.5GHz or AMD XP 1500+
# 1024 Megabytes (MB) of RAM
# 64MB 3D Graphics card with Hardware Transform and Lighting (such as an Nvidia GeForce FX 5700 class or better)
# Two-button scroll-wheel mouse
Looks like you have a 2.4Ghz celeron CPU, right? And 256mb of ram... you are adding 512mb you said, right?
Celeron CPUs were not designed with gaming in mind. They are good for browsing the internet and writting documents, but for gaming, the just don't cut it. However, the one you have should be OK to at least run the game with the settings turned down.
As for the new ram. Just to forewarn you, there is a chance that it may not work. I hope it does work, I really do! There is no way to predict. Motherboards tend to like you to have two sticks of IDENTICAL ram when you are using two sticks. You are going to be using two sticks of different sizes in there it sounds like. One 256mb and one 512mb. Hopefully they are are same speed at least? PC2700?
I'll take a guess and say that the card I link you to above would actually be a noticable difference from your current integrated graphics.