well for starters if im not mistaken MOST networks defult IP is 192.168.0.1 And that wuld be the routers IP addres. DON'T make a computer IP address that, it will never work.
So what you want is to set a static IP up with your Mac?
System preferences --> Network --> Advanced network (idk im on leopard but im sure it'l be similar in tiger)
click the TCP/IP tab,
next to configure IPV4 choose "Manual under the drop down list"
Now there should be empty text boxes it should look something like this:
Keep in mind things may be slightly different in tiger.
NEXT (the step that used to make this not work for me)
go to the DNS tab
and manually enter your DNS servers, you may need to contact your ISP for these.
if im not mistaken there is no DNS tab in tiger though, and instead there is just another text box in the screenshot I showed you, simply just put your DNS addresses there.