the cheapest and easiest way would be to get a hub/switch with at least 2 ports (smallest are 4 ports I think). The brandname doesn'T matter at all. Just go for the cheapest. It will work with any os and hardware. I think the prices are around 20Euro or so.
Anyway, I would suggest you to get a router. A router is a "little computer" managing the network and allowing the comps to have internet access. This way, your pc could be off and you can still be online.
I would suggest you to get a router with 4 port. Price around 40Euro here when it has no wireless access point. However, it might be important to know, what kind of internet connection you have. You might need the fitting modem. If you are on dial up 56k, you will need a 56k modem in your router. If you are on dsl, you will need a dsl modem included in the router or an external one plugged between router and your phone line. For cable connection you don't need any modem AFAIK.
Now, about printersharing: What kind of printer do you have? Does it have a network plug as well or is it just usb? I don't know how well printersharing works when it's plugged to mac and shared with pc. I just know that it works just fine when reversed.
And filesharing: share a folder on your XP machine and turn on Personal filesharing and Windows Sharing in System Preferences -> Sharing.
However, if you really have no clue about all the network settings, you should come back here and we'll help you out. Don't worry!