Yo no creo que sea "start up", que quiere decir "arranque", sino me imagino que están hablando de la pantilla en la que se puede empezar a proceder contestar las preguntas necesarias, o lo que sea. De todos modos, en las pantillas, se suele ver "start" y no "startup" (que debería ser con guión).

I would use this wording, as it seems most natural to me in English. It is not a word-for-word translation, but I think it works.

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Note added at 7 mins (2010-01-26 17:09:36 GMT)
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See, e.g., How to Create a Startup Screen with a UserForm

In Microsoft Excel 97, you can use a custom UserForm and a Visual Basic for Applications macro to create a startup screen (splash screen). This article describes how to create a custom splash screen for a specific workbook.

http://support.microsoft.com/kb/158848



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Note added at 10 mins (2010-01-26 17:12:09 GMT)
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When a user accesses the application it will know nothing about the user or their group. The application's first act must, therefore, be to direct the user to a 'log on' page ...

http://php-programming.suite101.com/article.cfm/how_to_use_g...

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Note added at 12 mins (2010-01-26 17:14:14 GMT)
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Here's some wording ("direct the user" ...) from Microsoft's website:

Use the Redirect method to direct the user to a different than the one the user requested, such as a different webclass or an external page.

http://msdn.microsoft.com/en-us/library/aa231199(VS.60).aspx

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Note added at 14 mins (2010-01-26 17:15:59 GMT)
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And from Facebook ...

Easier prompting for permissions. All you have to do is direct the user to a URL and prompt the user for the permissions your application requires. You can prompt for permission wherever appropriate in your application flow, or at login. A series of dialogs appears, one for each permission, and the user is free to grant them one by one.

http://forum.developers.facebook.com/viewtopic.php?pid=16388...

The PHENIX GUI will perform comparison tests and direct the user to a logical PDS workspace choice.

http://www.biochem.arizona.edu/xray/phenix-doc/wxgui/PHENIX_...



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Note added at 15 mins (2010-01-26 17:17:14 GMT)
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And from Google ...

Google will direct the user to a web page displaying a verification number (see example). The user must return to the installed application and enter the verification number.

http://code.google.com/apis/accounts/docs/OAuthForInstalledA...

Once you register, you will be directed to the initial screen, where you will be promted to describe (or "enter") the timeframe to completed/carry out the task/work/job.
I would not use "start-up" for this context, as it seems to me that you are talking about a program/utility on a computer already running.
Buena Suerte.