jav0,
I know you already got it working, and I apologize if you already know this stuff, but since you sound like a beginner, I thought the following might be useful to you.
For the record, brailian is right about my intentions with those 2 lines. Option statements should always go in the general declarations section. The Option Explicit statement forces you to explicitly declare every variable you use with a Dim, Private, or Public statement. You should always have it as the first line of every module you use, as it enables you to catch lots of typos and other errors. For example, if you had had the Option Explicit beginning your program but not the declaration for Counter, the compiler would have raised a "variable not declared" error when you tried to run the program, rather than just letting it do something you didn't want.
As for the Private statement, let me run down the scope rules real quick.
1) Module level variables: These are declared with Dim or Private in the General Declarations section. Every procedure in the module can see them and they last for the life of the module. (For .bas modules, this means as long as the program runs, for form modules, this means as long as the form is loaded.)
2) Local variables: They are declared with Dim or Private in a Sub or Function. If you use implicit declaration (as you did), then the variables in your Subs will be local by default. Then last only until the Sub ends. For event procedures, this means that the variable will be created anew every time the events fires, with none of the information being retained between calls.
The upshot of this is that your code was completely correct, except that the Counter variables in the Form_Load and Time event procedures were both local, and thus completely different variables. Remember that two variables can have the same name if their scopes are different, i.e. if they can't both exist at the same time. If you used the Private Counter As Integer statement in the general declarations section, then the value of Counter would have survived between calles to the Time event, and it would have worked perfectly.