Your video card might just not be good enough to run World Of Warcraft, and that is why it freezes when alot is on screen.
What resolution for you run the game at if you have to run all the settings on low?
It definetly won't be your RAM since this won't increase game performance much, or at all, only game loading.
1024mb is plenty and if your motherboard manufacturer says it won't support 2048mb (2 gig)...it simply won't. For any task 1gig is sufficent!
I run on 1024mb but have a Radeon 9800 Pro which runs the game at high settings with about 20-40fps in big areas... quite low for a card thats not that old, but is much newer than yours.
So I'd suggest you get a better graphics card, which is the problem.
The card you have is rather old and just might not be up to scratch for the job.
A nice Geforce 6600GT for instance would have this game running like wild fire, and would run all new games at rather high settings for the near future. It only costs about £140-£160 too, and so it worth the upgrade. If that card you have now has just been updated, you chose the wrong one I'm afraid for such a new game, and has no chance at running newer ones at high settings either
A Cable modem should be great at playing this game as we use one so it can't be this either
and tell me what connection speed you end up getting. We get approx 600 on this test which is definitley fast enough
Hope this helps