Also, is there a big risk of someone hacking into my desktop if I allow people to use my router.I want to offer free wifi at my apartment, but I want to lock the users to one website, can I do that and how?
Remember that if you allow others to use your router, any illegal action of theirs comes right to your door. Setting a forced homepage is not possible on standard routers. Limiting their use will be of no good to them. You will need to be extra careful of your security, and make sure your passwords are very difficult to guess, especially on the router.I want to offer free wifi at my apartment, but I want to lock the users to one website, can I do that and how?
I cannot answer your first question, but i'll try to answer the last part in regard to security...
First of all, make sure you access your router's set up screen (usually by opening internet explorer, and typing the ip address [i.e. 192.168.2.1]) and find the section about security.
I have my wireless router to allow network access, including internet, only to users using a specific password; I have a separate password for autorized access to my internet, which is different than the first one, and doesn't NOT give access to my networked computers and devices, strictly internet access. For instance if i have friends over and bring their laptops, they can access the internet by conecting to my secured wireless connection using the guess password, but they won't be able to access my network.
Specific instructions vary from router to router, so you're going to find out how to do this from the router's documentation or website.