the probes you are receiving are probably a mixture of the following:-

some will be from random windows machines on the net - as windows uses udp 137 to resolve netbios names. This should only happen on the broadcast domain i.e. internal network but you also get machines spewing this traffic out on the internet. Some machines will also try and resolve your name when you have browsed to them , if they are an nt /win 2000 server. A lot of this stuff could be considered 'background noise' and can be ignored.

There are a couple of worms which probe on port 137 i.e. Opaserv and Bugbear, which are looking for holes, but any half-decent firewall should block this traffic by default. Personally I use zone alarm, but I've also heard that tiny personal firewall isn't bad either....