How do I write good code to generate a random 6-8 character text field to be included in the email sent from my application to the user upon signup and have it be required to be entered in a web form before the user can actually use the site? (I can probably cobble something together, but this is important.) Thank you.

it would not have to be random. it could just be a sequence. the important thing is that you can recall the values that have generated and used. e.g. a data base table to query if a code had been generated and/or used and/or expired if there is a time limit for code use. However, I would use a GUID for this value.