I find new routers to have out of date firmware.
Try updating that then and if the problems continue return it as defective.
I just hooked up a Linksys Wireless G 2.4GHz router on a Gateway PC-Pentium 4, 3.0GHz and 512mb Ram. I'm now experiencing a major slow down or non-response in opening up programs, logging onto the internet, opening up email and spastic mouse movements (also wireless, but with two new batteries installed on 8/30). Anyone know what's up with this?