to CF
The link to your log doesn't work for me, but have you tried using the Shields up test on
www.grc.com?
A software firewall, such as Sygate, should be usually sufficient to deter random attacks, unless you have specifically opened up ports.
A router would definitely improve your security as by default they include a 'NAT' firewall which rejects all incoming unsolicited traffic. Try looking for a Linksys BEFSR41 on ebay if you are not likely to need wireless. If you think you ever might want to go wireless, the Linksys WRT54G would be a good choice.
HTH