The problem is a lot of "todays" Internet Security Suites are heavy on processing power and other resources on older machines.
In the past Ive used Norton AV (up to 2003) on older PCs without any problems at all.
I must admit I got a free version of NAV 2005 with a new laptop and I was extremely disappointed at how much resources it took up, so ended up uninstalling and replacing it.
If Im setting up a new PC or Internet connection for someone I normally use Avast for AV rather than AVG, and I prefer the Kerio Firewall.
However, I recall that you are using a router with a hardware firewall and behind NAT. If you are using the laptop at home behind your router its up to you or not if you think you need a software firewall too.
Put it this way, although I do have a firewall on my own laptops, I only switch the software firewall on when Im away from home.
When I first got adsl for the first couple of months I still ran a software firewall on all my machines, but after a while I realised that the hardware firewall in my router was catching everything first, and therefore as far as my own network was concerned the software firewall wasnt doing anything other than taking up resources on the PCs.
Over 3 years later and Im still happy to let my hardware firewall do its job. You still need AV though.
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*] If you do decide to do this, go to somewhere like grc.com (shields up) and do a security port scan and make sure it gives you the all clear first.
The only thing I dont agree with grc.com reports is that it may frighten you if it says it can see your IP address (so what?) and also I personally dont believe in blocking ICMP pings. This stops ICMP (which is a valid internet protocol) from working and in turn can *break the internet* for some users.
Details where you can get Kerio etc from
http://www.kitz.co.uk/security/software.htm[
*] Dont forget anti spy/malware