This is fairly undocumented piece of information which I have got from this blog

http://www.bluedoglimited.com/SharePointThoughts/ViewPost.aspx?ID=242

I havn't tried it myself, so I cannot gaurantee its completeness. I am posting it

here for the sake of interest and community .....

In the web.config file in the Sharepoint virtual directory contains the following section:

<Sharepoint>
<SafeMode MaxControls="200" CallStack="false" DirectFileDependencies="10" TotalFileDependencies="50" AllowPageLevelTrace="false">
<PageParserPaths>
</PageParserPaths>
</SafeMode>
:
</Sharepoint>

By default the node <PageParserPaths> is empty. You can add <PageParserPath> nodes to specify the

virtual paths where you want to allow server side scripts:

<PageParserPaths>
<PageParserPath VirtualPath="/pages/*" CompilationMode="Always" AllowServerSideScript="true" IncludeSubFolders="true"/>
</PageParserPaths>

Where CompilationMode is one of the following values:

Always

The page should always be compiled (default value)

Auto

ASP.NET will not compile the page, if possible.

Never

The page or control should never be dynamically compiled.

I assume that the AllowServerSideScript and IncludeSubFolders flags speak for themselves.

Be careful with the virtual paths you specify in your PageParserPaths. Anyone that can modify or add a page to the virtual path can insert code that will be executed server side with no restrictions.

A good location to specify as a PageParserPath is the location where you store your masterpages, for example /_catalogs/masterpage. You can now add server side script to your masterpages, which makes it available in all pages using this masterpage.

<PageParserPaths>
<PageParserPath VirtualPath="/_layouts/masterpage/*" CompilationMode="Always" AllowServerSideScript="true" IncludeSubFolders="true"/>
</PageParserPaths>