As cheap as you can pick up a router on ebay these days its Crazy not to have one; even for one pc, just for the hardware firewall.Of course good software antivirus protection as well as popup blockers and something to remove spyware is a must.
I have found frequent scans to be very helpful.
I am using AVG,Ad-Aware SE,with a hardware firewall.A browser that scans email is also a plus too.I am using MSN Premium
IBM T22 laptop,900mhz p3,20g hdd,512mb ram
IBM Netvista M42 40g hdd,1.8g p4,512mb ram
IBM Netvista 933 mhz p3,10g hdd,256 mb ram
Winbook laptop 400mhz p2
Dell 4600 2.8g cpu,120g hdd,256 mb ram(On bottom of list where pc of **** belongs)
768/128 DSL w/LAN(wireless G)