Some of the problem seems to be that you don't really understand the environment. Every one of the errors that has confounded you stem from scope (visibility) problems.
For instance, "Me" is a shortcut that exists only in what Access calls "documents" - forms and reports - inside of things that are coded. And only when they are coded. Further, "Me" means different things depending on where it is encountered. Yet it always means the same thing. That's because it is a shortcut to the currently opened document in the Access sense of that word. I.e. an opened member of the documents collection - which can be either a form or a report.
The "parameter" bit comes about either because you have spelled something incorrectly OR the thing you named isn't visible at the time. Whenever Access has to evaluate something that it can't find, it assumes that you have named a parameter, so it asks for it. Therefore, whenever you see that kind of error message, look for the thing you named to not be open or not have the name you see in the parameter dialog box.
The issue with changing (or not changing) underlying data in a table when you used a field for lookup relates to not realizing whether the data was part of the active recordset for the form. If you are going to search for data that is in common with a lookup table and the working table you are populating, look at some of the "Combo box" or "List box" wizards. One of them includes a way to have the box look up a related record. If you look it up from the wrong table, you start changing things that you might not have wanted to change. This is where the combo box wizard can help you.
All of these things tell me that you need to find a good Access textbook. If I knew one, I'd name it - but my wife teaches this stuff and she has yet to find a book she likes.
OK, this criticism doesn't solve your problem.
Scott's instructions were fairly clear. I strongly suggest you return to the sample code that is part of this site and also use the Search feature to find more examples of "Cascading Combo Boxes" as a way to get you going. If you can find an article by Pat Hartman, you will be ahead of the game. She's good at what she does. I regret that I don't have my reference books with me right now so I can't be more specific in my suggestions.
