Yup You can advertise Software, But they must not be counterfeit or Bulk email software. For more details visit: Google AdWords Advertising Policies: http://adwords.google.com/support/aw/bin/static.py?hl=en&page=guidelines.cs (Choose Policy as Content)
An easy way to find your answer is to do an organic search on Google on the keywords you planning to run advertising on. If you see other advertisers' ads, then most likely Google do accept the ad.