need help making a "bot"

hi guys,
this is the first time i register a forum and ask for help, but i cant find anything usefull on the internet or forums that can help me do something like what i need :\
hopefully i'm not posting this on the wrong section too :p

i play a game were to pick up stuff u can press Z key, what i wanna do is a "bot" that auto picks my stuff (dont wanna download hacks from sites and i though this was easy to do u.u )

i made a program to spam Z but i cannot make it work when minimized

What i am trying to do is:
-When pressed F7 it starts the program (cant get it to work with F7, i had to add a button, so maybe another key)
-Random *V1 from (40-60)/100 (EXEMPLE: V1=55/100= 0,55)
-Use the value of *V1 to press Z after 0,55 secs
-REPEAT untill F7 pressed

its that easy BUT i cant get it to work when i minimize the program :\ i can get it to spam Z on a Box but it doesnt work with milliseconds nor on other programs, when i minimize it stops.

PS:i wanna randomize the time to make it untraceble to GM's, if its 100% of the times 0,50 sec is obvious that i have a aid program x)
Any ideas? is this possible using VB?

so i made it to work if minimized and the code i have right now is this:

on the timer

Code:

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Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerval.Tick
        My.Computer.Keyboard.SendKeys("z")
    End Sub

---

This spams Z, but with manual INTERVAL, to random the interval i tryed this

Code:

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Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles timerval.Tick
        Dim Ran As Random
        Dim num As Integer
        Ran = New Random
        num = Ran.Next(500, 2000)
        timerval.Interval = num.ToString

        My.Computer.Keyboard.SendKeys("z")

    End Sub

---

cant get it to random the interval bettwen 60 milliseconds and 200 milliseconds (the "500, 2000" was a test)
any ideas?