Ok My ADSL has been working fine since I installed a home Network around 4 months ago. However the last 2 days it can only be described as eratic.

It will randomly bring me 'DNS page may be experiencing technical difficulties/page not found' on pages I know are up(note: this is usually when I click on links), at the error page the website will usually work when I click the URL bar and press 'enter' effectivley refreshing the page I have no idea why it suddenly works when I do this. However some webpages are still refusing to come up.

Also MSN messenger is randomly not stating up only to start perfectly fine when I try a second time.

My network consists of a Netgear Router/Modem connecting three computers (one of which is a laptop) to a 576kb ADSL line.

Can anyone help me with this?

Check the DNS-settings in your router. Maybe your ISP has changed them without notifying you (happened to me). Also check the Internet Protocol TCP/IP settings that they still point to your router.
Empty the filecache on all machines.