Please!!--Problem with my Mac vs other users!!!

Hi all.
See, I have this problem.
I have a linksys wireless router, but for the most part we're not using the wireless.
When I bypass the router entirely, plugging the cable from my ISP directly into the back of the Mac, I run fine, really fast.
But if I plug into the router because of needing to share with other users, my brother's PC, my nephew's x-box, or occasionally my brother's wireless dell laptop from his job, my Mac grinds to a slow crawl. It works, but like a
33.6 modem. As a matter of fact, it crawls even when noone else is using, as I just checked now. Any time I'm in the modem.
Can anyone tell me why this is, or what I can do to remedy it?
Is there some configuration with my Mac or the modem?
Thanks so much,
webmeist

Do you have anyone else, say a neighbor maybe, that is sharing your connection when your router is plugged in??

You can also try resetting your router to factory settings and try it again (remember t secure it).

I suggest you try a different wireless channel on the Router - you may be colliding with a channel somebody else is using.