Every time i scan a range of computers on a network it simply kills my connection, even though it still works and says its scanning i can;t browse the internet after a while.
Is this normal? And is there anything i can do about it?

How many parallel threads are you running and what sort of a connection do you have?

Well, in nessus i have "number of hosts in parallel" set with 20 and then I decreased it to 10 and 5 checks in parallel. I was thinking that it could be that i have a cheap wireless router?
Also the same thing happens with nmap when it scans and shows all ports as open, i guess all the probes to so many "open" ports crash my connection. Also when i specify only certain ports it happens rarely that my connection floods.
Basically the scan continues and never stops its just that i can't browse the net anymore and when i stop the scan i cant browse either, only a restart seems to help.
Should i just buy a new router, and if yes then how is the
LINKSYS WRT54GL ?

Couldnt be your router. Well it could...but its very rare.
Are you behind a firewall while doing the scan?

Yea actually i am the routers firewall, maybe i can set up DMZ .