Stéphane,
You are missing an important point of ASP.NET programming. You need to get away from the code-embedded-in-html ways of classic ASP. It's particularly applicable to your image. If you need a programmatically modifiable image tag, use the asp:image control and runtime code to change its image url:
<asp:image id="imgLogo" runat="server" />
Runtime code (perhaps in page_load):
imgLogo.ImageUrl = String.Format("{0}/images/{1}/LogoMain.gif", GetDistributor(), GetLanguage())
This makes all parts of the code much more readable and follows the proper programming model of web forms.
You can do the same thing with your div tag. However, because there is no div server control in .NET, the control will be an HtmlGenericControl:
<div id="divTest" runat="server">
Runtime code:
divTest.Attributes.Item("style") = GetStyle
If you follow these guidelines, you shouldn't experience VS.NET interfering with your markup and you'll have much better luck overall when dealing with web forms.
Peter
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Work smarter, not harder