need to share internet connection between windows pc and mac

The bottom line with your question is I don't know, however if you live in the UK & get your internet from BT their wireless hub you can connect both via Ethernet.

We have my Mac my old PC & my wifes lap top (wireless) connected to it & they all work fine.

If your not in the UK I'm sure you can get the same??

 

buy a switch (or an access point if you want to go wirelessly)

 

Both XP and OS X allow you to share an internet connection. However, they tend to be fairly slow and unreliable, the XP setup is very unstable. You really need to buy a router, they are cheap and simple enough to configure. Technically, a switch won't do it unless your cable modem is capable of acting as a router.

 

Do both have wireless you could run an ethernet cable to one and share the connection through your wireless card. Though this would be a bit of a pain to set up.

If the laptops have wireless connection you can get a wireless router for fairly cheap. It also has wired ports on it.
http://www.newegg.com/Product/Product.aspx?Item=N82E16833122016

If they don't have wireless or you don't want to spend the money a switch is really cheap.
http://www.newegg.com/Product/Product.aspx?Item=N82E16833166006
Plus add a couple of ethernet cables
http://www.newegg.com/Product/Product.aspx?Item=N82E16812118007

You could save even more money on a wireless router by getting a refurbished one through pricegrabber or checking out ebay for a used one.