Problem or not?

I have a D-Link router and one computer that is conncected to it with a wire and the other computer is wireless conncected. I have the standard windows firewalls. One of my computer is not working right and I am getting ready to reset it. I was wondering if I needed a better fire wall or some type on network security? Also if I do how would I go about setting it up. Not sure if I set up the network right and was wondering if any could help me make sure I set them up right and make sure that they are secure. Also if there any I can do other then make it so they can use each others documents and shared documents. Mostly worried if my computers are secure with my wireless router and no one else can axcess my files. I basically set up a net work and right clicked documents and went to sharing and clicked allow network users to share and change my files. then ran all the set a network up wizard stuff, and scaned for computers on my network and it put 4 files in my network place both computers documents and shared documents. I did not set up any security up my self other then avast and spybot search and destory. So I was wondering if any can tell me I if I set them up right, what else I can do with a network, and about security.

 

May be this can Help.

Basic Protection for Broadband Internet Installation.

Assemble a Freeware Security suit for Internet Connection Protection.]

As for File Sharing.

Successful Sharing involves some general consideration in Network settings, http://www.ezlan.net/sharing.html

As well as specific adjustment of each computer according to what is allowed to be shared.
http://support.microsoft.com/default.aspx?scid=kb;en-us;304040

 

what is a good free software fire wall I can use.

 

ZoneAlarm which is available from MajorGeeks:
http://www.majorgeeks.com/ZoneAlarm_Free_d388.html

 

Can any 1 tell me how to set IPs that are allowed to share files with zone alarm?

 

what I mean is how do I set up the Trusted Zone to only allow my 2 computers? Also my Dell is using Windows XP SP1 and the other computer is using SP2. My friend told me that it is legel to use the SP2 disk on both computers just as long as I don't use the same both different product key numbers. Is that true or should I use the dell disk for the dell before I reset it and not listen to what me friend told me?