When I install tunexp from my wpi, and then run taskkill from my wpi script it runs to fast. Tunexp runs after taskkill is done. Is there som way to slow down taskkill from my wpi script?

I'm not familiar with TuneXP or what you are trying to kill, but there are a plethora of ways to do this. You could:

~repackage/hack/recreate the installer so as to remove offensive window entirely (can be a lot of work, doesn't always work)

~make an AutoIt script that waits for the window with a certain title to open, then closes it.

~use start /wait to call the installer. This will only work if the window you want to kill was spawned by the installer, and is not the same process.

~Find/download/use a commandline tool called Wait.exe and wait a set amount of time, then use taskkill (only useful for very simple and fast installers that you can easily estimate the time you need to wait)

~use NirCMD to wait a specified time, then use it to kill the window (you can kill by process name, window title, part of a window title, handle, or even just the "top window"). This has the same restrictions as using Wait.exe, but has the advantage that it doesn't need to open a cmd.exe window of it's own (use nircmdc.exe).

...

AutoIt is the all-in-one solution, but seems "overkill" to me for killing the simple things. What you should use really depends on the situation, and whether or not you're willing to look into other options.