Are you using USB or ethernet interface?? If using USB, fucking bin it and use ethernet
If your laptop is only downloading at 30kb/s as well then it cant be a fault with your pc can it?
Check all your filters, unplug any extensions and try it. You might be getting line noise from an unfiltered extension (sky box, redcare etc)
The BT HomeHub's are shite though, bodged up thomson speedtouch firmware that they've managed to make even worse.
Installed one for a mate, pc over USB (didnt have a ethernet card in the pc at the time) wouldnt connect to the internet unless laptop was connected over wireless. Disable wireless on the laptop and the PC loses internet altogether. fuckin explain that one
Buy a Linksys router, then you'll know for sure if it's a line/internal wiring problem. I don't trust BT routers as far as i can throw them, and believe me i've wanted to many a time
Also, your line may sync at 4mbit but you may not get anywhere near those DL speeds. But 30kb/s is extremely low.
Mine sync's at 1mbit but only downloads at max of 80kb/s because i'm fuckin miles away from my exchange in the middle of a field