For those of you who are unsure of weight, or are making trips to the post office to weigh things, I highly recommend investing in a postal scale. They're really cheap, around $20. You can get them at any office supply store or directly from the USPS web site. Between the scale, and the USPS "click 'n ship" program, I NEVER have to go to the post office. When I first started on ebay, I spent hours every week in line at the PO. It's SO nice to now be able to schedule a pickup, and have the postman just pick it up at my door.
Also, Jana, I have been using tracking and insurance on envelopes for years. I've never been told that this can't be done. Check the rules and regs on the USPS web site. I've found that the postal clerks often hand out misinformation, or contradicting information. If you have a good relationship with the clerks at your post office and don't want to start an argument, you might try shipping from home (handing the letter to your mail carrier) and see how it goes.
Kathy
Kathy