help please with problem setting up network with Thomson 4 port router

[#1]

I've just got round to changing the IP settings as described above for my PC's access to the Thompson router.
I changed the IP of my PC in Internet Protocol (TCP/IP) Properties from 192.168.1.2 to 192.168.1.64 (Will change my wife's to ...65 later).
I then changed Zone Alarm to show the new Trusted IP Range from 192.168.1.2 - 192.168.1.3 to 192.168.1.64 - 192.168.1.65.
All worked well.
As a test I changed the Zone Alarm setting back to it's previous setting and still had internet access. I reset Zone Alarm and set the IP address for my PC back to ...2 with same result.
I was expecting that if Zone Alarm's settings did not match those of my PC that I would not be able to access the internet. Or have I misunderstood how this works?
Also, while the both Settings have been changed when I try to access My Network Places (subsqeuqently Shared Documents on my wife's PC) it causes explorer to crash. Change both back again and all's well. Any ideas why this should happen?
Thanks.
Edit: Was this a case of 'If it ain't broke then don't fix it'?

[#2]

Have you turned DHCP off on the router? Allocating fixed IPs which clash with those set by DHCP is potential disaster and could be the cause of the Explorer crash. An alternative to turning DHCP off is to avoid the DHCP range, i.e. allocate IPs not above 192.168.1.63 with the Thomson.
The router netmask covers any 192.168.1.* IP so it will happily route any connection from within that range to the Internet and back or within the local area. As far as ZoneAlarm is concerned the router is in the Internet zone with either Trusted range, so it makes no difference which range is specified - if Internet access works with one then it will work with the other.
There is no reason why the PC and laptop couldn't have retained their previous fixed IPs. No changes to ZoneAlarm settings would have been needed.

[#3]

Thanks for the reply spraxyt.
I think I got myself confused after re-reading this thread earlier today and thought I should change my PCs' IP addresses to the range 64-253 whereas it seems that 2 to 60 is fine.
I'm not too familiar with DHCP - is there a good source of info on this I can read up on?
Thanks again.

[#4]

Try this from Good Ol' Wikipedia

[#5]

Thanks