Im having a problem along those lines. Its strange, my connection is absolutely perfect when there is only one device (PS3, XBOX, PC) active. For example, my dad was playing COD:MW2 on PS3 and had a rubbish connection (i have the same problem with my PC, but its so bad that the connection actually drops for 5 seconds every 2 minutes constantly), but when I turned my PC off, leaving the PS3 the only internet connected device on in the house, he had an amazing connection. I too am using a Belkin Router, and ive also contacted Belkin and had a nice 3 week long chat with them. I got the router replaced, but it made no difference. I think I can safely say that it isnt a problem with your router, but it is a problem with your other devices. They may have the same IP. Ive just changed my IP on my PC prior to typing this, but it has made little difference. Anyway, I hope an answer to your problem will solve my problem.
Ill leave you with a suggestion. Now, this may or may not work, but renewing your IP might solve your problem, but it didnt solve mine. This WILL NOT harm your internet connection, so dont fear it. Here goes.
Ok. Go into "command prompt"
Next, type in "ipconfig", without the speech marks, to view your current IP, DNS, and Gateway key.
Now, type in "ipconfig/release", without the speech marks, to disconnect your computer and "release" the IP from your computer. Wait about a minute, then type "ipconfig/renew" without the speech marks.
You should regain your connection and your IP should be changed. If not, then there is another, slightly longer way of changing your IP.
Please note that im using Vista, so my menus will be different from yours.
Goto "Control panel" then "View network status and tasks" then "View Status on your Wireless network connection. Then hit "Properties" and double click on "Internet Protocol Version 4", or "6" depending on what your IPCONFIG tells you. Now click on "Use the following IP Address" and enter the first 3 sets of numbers (194.243.2.###) outlined in your IPCONFIG. For the last 3 numbers, enter anything between 1 and 225. Next, enter your Gateway key outlined in your IPCONFIG into both "Default Gateway" and "Prefered DNS server". Dont worry about "Subnet Mask" as it will generate its own key. Now click OK at the bottom and close the windows, keeping Command Prompt up. Now type "ipconfig" to verify if your IP has changed. After that, its just a wait to see if the problem persists. I hope this helps you.