By safe, do you mean from attacks by unscrupulous 13 year olds?
Several things you can look into if that's the case. You could buy a DHCP router that has some built in security. This could be moderately expensive, but (I think) may be the solidest solution without turning yourself into a full-fledged IT admin.
A more practical solution, budget wise, is to use the built in Firewall in XP (assuming this is what you're using) and another firewall. Just do your background research before you make any hefty purchases. I'd suggest tiny software's firewall (www.tinysoftware.com
) as one to look into and disuade you from any Norton security products.
Hope this helps you some, but if this isn't at all relative to your question, just post again.