It is normal that when you step into Hyjal, your fps decreases significantly when the trash waves appear and even more so when your hunters kite a mob to bring in other npcs like jaina or thrall/taurens. However it's of course not normal to be disconnected. Quaza above has already mentioned some stuff which you could look through, but one thing that you can look into is your network card configuration. That was the one that made me disconnect tonnes whenever I had an overload of information and after making the change as posted in blizz's forum, it was solved.

This is what I have gathered from the blizzard technical support. I was using an Asus Mobo, so the settings might be a lil different but this is pretty much the gist of it:

1. Go to "Start" > "Control Panel".
2. Double click to open "Network Connections".
3. Right click on your network adapter and go to properties (should be labeled as "NVIDIA nForce Ethernet Controller").
4. Click on "Configure" and go to the "Advanced" tab.
5. Select "Checksum Offload" or "Hardware Checksum" and choose disable in the window to the right.
6. Select "Speed and Duplex" or "Media Type" and select "Force 100 full duplex" (Note: if you lose internet connectivity, select "Force 10 full duplex")
7. Click on Ok.

You may also need to delete your entire WDB folder (located in the World of Warcraft directory) and test the game. The cached files in this folder are occasionally known to cause this issue, and their deletion may immediately fix the problem. However, unless totally necessary, dont do this coz you will have to redo your macros/keybindings and all which might take some time.

Last but not least, dont play in windows mode unless really necessary. Your fps will increase significantly with your full-screen play.

Some other things I do during 25-man raids :

1. Nag guildies who have Recount syncing option to turn it off. You can check using a FuBar addon called "AddonSpam" that will give you a list of addons that pulls data from you.

2. Turn off sound.

3. Tone down my graphic settings.

4. Turn off Scrolling Combat Text feature/addon.

5. Turn off names of NPC + my names + others + guild names.

6. Turn off addons that take up huge memory resource e.g. Cartographer, Group Calendar, Gatherer, Auctioneer. Basically addons that I don't use for a raid, it gets turn off.

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Added on November 23, 2007, 11:22 amprobably what i need to do now though is to buy a new modem.