i really want a new iMac but can't afford it right now. so i was thinking of getting an older iMac to replace the pc we have now. if i do do this can i use the wireless router that i have now with an iMac G3 or G4?
If you want the wireless to be an internal component, yes. Another opton is to get a USB wireless adapter that is known to work and be recognized as an Airport. There are a few out there. I don't remember off the top of my head. I know i used to use a d-link back in the day that was seen as a native Airport card by OSX.