It is worth buying a router though, especially if you have more than one PC, as using one of your PCs as a router puts an unnecessary load on that one PC. If your network comes under attack, the PC that is acting as a router can be put at risk, it could be crashed or slowed down and find that all its RAM is being wasted. Hardware separate routers almost always act as firewalls too, which is an extremely good thing as they keep the incoming badness out of your LAN and, as far as possible, prevent incoming junk from crippling any of your PCs.
I would say that not using a separate hardware firewall/router is unsafe if there is any chance of you being attacked. Don't say, “but I'm not important, no one knows who I am, no one dislikes me”, as a great majority of current attacks are mindless scans carried out by computers with no human behind the attack, not unless the scan penetrates a network and finds something juicy, in which case a human might come and take a look.
But having a PC which from time to time runs really slowly, like a dog for no apparent reason, is not a good thing, and having to deal with a load of network traffic or even an attack, is not a good state of affairs. Superb routers can be had for peanuts.
For example, take a look at the
Zyxel xDSL modem/router/firewall/WAP that is available from the Andrews & Arnold shop (
http://forum.kitz.co.uk/index.php?topic=16494.0) - you don't have to be an Andrews & Arnold customer, the shop is just a reliable source for cheap, high-quality,
reviewed kit.