Problems with my internet connection?

[CapAIM]

I have a cable modem connected to a wireless router. Over the past month, I've noticed some problems with my wireless internet connection. The connection speed is very slow and it takes forever for web sites to load and files that I try downloading often time out. After a few days, the connection crashes and goes into "limited or no connectivity" mode but when I reset the modem and the router the same problems occur, slow internet-"limited or no connectivity" mode after a few days. At the same time, I noticed that one of my neighbors has also set up a wireless network (that I sometimes use when mine crashes) Is it possible that my neighbor's wireless network is causing problems with mine? I've only started to notice these problems when the neighbor's network appeared. How can I fix this?