Well, you are on quite a dodgy ground here. The majority of freeware sites I know, fail to comply with Adsense policies. However, if you are 100% genuine, you should be OK. It's just as your site grows bigger, it will be hard to track all possible problems. You must not distribute warez or any programs that may infringe on copyrights. Also check if a 3rd party (you) is allowed to publish these free trial programs. There are programs out there that can be distributed only by its author, even if it is freeware. If what you're doing is legal, you can use Adsense.