I have a Macbook OS X 10.5.8 and use a wifi network that my whole household uses. The internet (browsing and while playing World of Warcraft) goes EXTREMELY slow. My dad who uses a more recent version of the Macbook (the silver ones or whatever) says he doesn't notice a slow internet even though we use our computers in the same room.

I updated all my software but the internet still runs slowly. What can I do?
Additionally, I read that plugging your computer directly into the internet source helps but I am unable to do that so is there any sort of way to get a second "source" for a wifi network without having a second network?