Help me choose a hardware upgrade!

I have about $400 to drop on an upgrade to my rig:

CPU: AMD 64 3500
GFX: ATI X850 XT PE
RAM: 1GB Corsair XMS 2-2-2-5 (2 x 512MB)
HDD: 2 x Hitachi 7k250 in RAID 0 array
SND: Creative X-Fi
DISP: Viewsonic 19" LCD
SPKR: Logitech Z-5500

I mainly play World of Warcraft and surf the Internet. I would like my computer to generally perform better, especially switching from WOW to Firefox and back. Which do y'all think would be the best upgrade?

Replace the RAM with 2 1GB sticks? (I probably would not be able to get a 2-2-2-5 again, so it would be an actual decrease in latency for me)

Replace the processor with a dual core? (Do dual core processors really help out with multitasking a lot?)

Replace the HDDs with 2 Western Digital Raptor-X (150GB) array? (Would they be a lot faster than my 2 7k250s?)

Thanks for any insight.

Looks like u got a nice system there =)

Your cpu is nice and enugh want more? overclock it!
Sure dualcore will/would help but it dosnt look like you need it (from what your using)
1Gb of ram is enugh for what u do more is allways nice but as u said yourself you prob have to drop timings and get WORSE fps (again like 1-2 fps ).
2x raptors is faster but not much you cut windows loads with 2s and wow starting in 0.5s less ...
Worth it? neeh

GFX? sure you will gain some if you get a 7800 or 1900 but for WoW it should easy be enugh for what your LCD can handle (1280*1024 I guess?)
If your going higher and still want to have all on then a switch on gfx would make a diffrence.

Clean up your system and get rid of all little mumbo jumbo stuff going on in the background. Use Bootvis to get a faster boot process and save your hard earned gold for some the new am2 (if the gains is big enugh)or parhaps intels new little toy (when it come out and if its THAT good as it might be)

Butt then again if the gold is burning then go for more ram and a better gfx

Thanks for all the help guys. I'm surprised that y'all think my X850 XTPE needs an upgrade. I was really planning on saving that one until Vista when I can get a DirectX 10 compatible card. Plus, the only game I really have problems with at my monitor's max resolution (1280*1024) is F.E.A.R. I'm really into WoW lately, and even my roomie's 9800PRO runs that game without a hitch.

I think I'm going to get a 2*1GB set of RAM; I can live with the 1-2 fps drop if my comp can switch from WoW to Firefox quicker. WoW takes up about 450MB-500MB, and Firefox takes up about 80MB-100MB of system memory. Considering that both these programs would probably run at the same time on 512MB RAM, they are probably scaleable, and I don't think it would hurt to give them room to stretch and swap over 2GB.

First things first though, I'm going to try to limit the 42!! processes that are running. I'd never heard of Bootvis, so I'm going to give that a try too. Thanks again everyone!

Bootvis : try it and mesure boot time before and after
I got a nice faster boot from it. Cant say that that will go for all but I think most will...

GFX : again for your LCD and 1280*1024 what u have is way enugh
You WILL get a better fps with a new topline card but its mesurable fps (from benchmarking) and not somthing u will notice much.