Slow internet speed

First of all, hi to everyone, I'm new to this interesting forum and my first post is of a big problem I have!

Ok, I know. There is a load of information about this issue, but here I am. I can't solve it! and it is driving me crazy, completely crazy

Around 5 months ago I got my new 24" imac. What can I say about it? I just love it, it is just perfect!. I have never ever had a problem with it, my internet speed has always been really quick! but...two weeks ago things started to go really slow, I did A LOT of research on this and I was surprised to find out that this problem is quite common. Anyway, I tried adding DNS (OpenDNS and even DNS I didnt even know), cleaning cache, deleting the airport log...I dont know...I just have tried everything! but my internet is still so freaking slow .

I have got 8MB broadband, a month ago my download speeds were of 600kb/s now the quickest I can get is 46kb/s (and that's being really lucky). I have two more laptops (both running wxp) and a ps3...my internet works PERFECT on all of them, I dont have a problem with it! but with my imac... ...I have tried everything and i dont know what to do....

Please anyone got any ideas? I am desperated.

Well, a place to start:

You said this started 2 weeks ago so -

1) What were you doing on your computer about two weeks ago just before and when about this happened?
2) Did you install and software (antivirus, or any kind of tool to monitor or modify your net traffic)?
3) Did you mess with any settings, including but not limited to your settings in safari (ie: proxy settings)?
4) Were there any updates in that time that were installed? If there were, what were they? (I know some people think an OS can't affect net speed, but it is possible because of the way the data is processed by the OS and the specific driver for an ethernet adapter - I'm not saying there is something wrong with the OS or the driver, I have a mac pro and it is fully updated and it works as fast if not faster then my wifes suped up gaming rig for surfing the net)

If its some sort of DNS related issue as many believe it is - this thread I stumbled across may help you get more data:

Extremely Slow Internet with Leopard - The macosxhints Forums

You may also want to confirm it's not a problem with safari and get firefox and see if you still have slow response times.

Hope this helps

I am using firefox and have the same problem:
Also have a brand new IMAC 24"