It looks like your dropping connection maybe due to interference, try changing the channels in which your router broadcasts. 1, 6, and 11 are the one's you should try first. If you dont know how to get into your router settings, find the make of the router and check the website. Also typing in your default gateway in a web browser lets you access it. 192.168.1.1 is usually the default for dlink and linksys. If you dont have a password set its usually admin, or just the user name is admin with no password. Try that.

Thanks, but when I tried another router than linksys/WRT54GP2, everything works just fine.

yes but are the channels the same? Some channels drop more readily then others.

yepp, same channels. Pure http, ftp and other "pure" internet protocols are never dropped. But linksys seems to have a problem with routing of wireless windows networking.