Tracking the open rate is nifty and I do it, but for 50 peeps, I wouldn't worry about the open rate, and use google analytics and the google url builder
to track click thru's, which matter more than the open rate. You could even easily, for such a small group, modify the url tracking code to track each individual email to see exactly which potential customers clicked through.
As for programs, for 50 peeps, if it's a one time shot, I would probably use outlook, create a template of the email, and send them 1 at a time. I have seen lazy people put the entire list in the BCC field and then list themselves in the to field.
If your gonna stay small for awhile, check out group mail 5.
If email is a big part of your marketing programs, then it's worth it to upgrade to a service provider like the post above mentions. I use constant contact and they aren't bad. I have used several others, none in the previous list thopugh, and they were all comparable.