Kerio version query

I am thinking of installing Kerio firewall on my Home PC. However, I am a bit confused as to which version. I have both versions 4 and the older 2.1.5. Which would be better?

Thanks,

My System details are :-

PC : Compaq Presario P4, 256 MB RAM

Windows version : XP-SP2

AV : AVG Free 7

Other protection software installed : DiamondCS ProcessGuard Free 3.405. About to install Ewido Anti-spyware 4.0 background scanner too.

Current firewall software : Apart from firewall in broadband modem provided by ISP, using windows firewall

Internet connection : Broadband. Also, falling back on dial-up when broadband is down.

Spam filter software installed : No