is it worth upgrading

Hello everyone i have a question i'm multiboxing 3 toon's on wow with a 20fp's in org with low graphic settings and was wondering if upgrading from 3gb to 4gb of memory and upgrading my video card to something better would fix my lag problem's or should i build me a new pc. Now keep in mind i'm sitting on a 450 dollar budget here for
new video card and another stick of 1gb memory.

[Ualaa]

Getting a 64-bit version of windows, will let you use more than 3.2GB of total system ram.
With a 32-bit version, you won't see much beyond 3GB of total ram (system ram + video ram, etc).

Win 7, Home Premium, 64-bit lets you use up to 16GB of ram.
Win 7, Professional/Ultimate, 64-bit lets you use up to 192GB of ram.

It's impossible to know where the bottleneck(s) in your system are.

Open the task manager and see if your CPU is maxed.
Open the task manager and see if your memory is maxed (less than 100K available.)
Download GPU-Z and see if your GPU is maxed.
Check your latency and see if that is too high (I typically see between 80ms and 100ms)
Consider buying an SSD. They are expensive, but give a huge performance when multiboxing.