I do not run a AV on my windows computer and it has been virus free for some time now... however i will never advocate not running it... My windows computer is set up for one purpose to play online games and it is set up with a static ip address in which their are massive acl's on my router to...
bosn netsimulater by my experience is by far the best out there... however it does have it's problems and such. The only way to get good exsposure to cisco equipment is to work on the equipment itself.
so i am going to take a wild guess here and say if you are connecting to the dsl modem just fine... try using a standard patch cable instead of a crossover cable