Why is my Internet Slow at times?

I've had my computer/Internet since the beginning of the last year. I'm on Virgin Media/ telewest. Since thursday my Internet has been playing up a lot. It'll mainly happens during the day, around the evening it runs normally. I can still download music and talk to people on MSN but when I go on the Internet it can either take ages to load up or not load up at all. I have an Symantec Antivirus program and always scan my computer once every week. It found no viruses but I do get a message that comes up saying -

'SYMANTEC TAMPER PROTECTION ALERT

Target: C:\Program Files\Symantec AntiVirus\vpc32.exe

Event Info: Open Process

Action Taken: Blocked

Actor Process: C:\Program Files\Windows Defender\MsMpEng.exe (PID 928)

Time: 20 April 2008 20:47:02'

What does that mean? Please can someone explain to me why all this is happening and how I can make my Internet run normally again?

Why is my Internet Slow at times?triumph

Its like travelling down the Motorway if no one is using it you can go fast, if everyone is travelling then you go slower. The same with the Internet the more people who use it the slower it gets. Hope this helps.

Why is my Internet Slow at times?worms

The day is a peak time for people using the internet. Because there is a lot more people using the internet at this time, the exchange cannot cope a full speed all the time. There is nothing you can do to stop this :( One thing you could invest in is called OnSpeed. Type it into google. It speeds your internet up but depreciates picture quality. You could also tell your ISP (Virgin Media) that you are unhappy with this and you never know.