Our router keeps dropping Internet/WiFi connection.?

We have 4 computers, one all-in-one WiFi printer, iPad & an iPod touch. Recently our network connection kept dropping whenever we would try to download large files from the Internet or open large pages. I can't update my laptop's iTunes because part way through it stops and gives me an ip address conflict error. I tried printing something off to day and the printer cut off the WiFi connection midway through the printing job. 2 of the computers are attached to the router via Ethernet & the other two are WiFi. We are running a netgear router. We also can't transfer larger files from one computer of another with out it dropping and giving us an error