If you're looking to remove the info left behind by a time limited trial program so that you can start the trial period again, then you might have some trouble. They try and make it very difficult for obvious reasons.
As for knowing when you're e-mail has been read, linney is exactly right but keep the following in mind. Not all e-mail clients support read receipts, and it's up to the person that you send an e-mail to whether they wish to send you a read receipt when they read your mail. Normally if you request a read receipt, their e-mail client will pop up asking them if they wish to send you one. There's no full proof way of doing it, for privacy reasons.
Hope that helps,
Daniel