This article explains how to run 32-bit versions of AspDotNetStorefront on 64-bit windows platforms. Note that this article provides instructions on how to run the .NET framework in 32 bit mode on a 64 bit platform. To realize the benefits that 64 bit computing offers, you must use a 64 bit version of AspDotNetStorefront. 

ML 8 versions 8.0.1.4+ and MultiStore versions 9.1.0.1+ run in 64 mode 'out of the box', so do not require any special handling on 64 bit systems. For earlier versions, use the directions below.

As published in Microsoft's KB at http://support.microsoft.com/kb/911720: 

1 - Open a command prompt by clicking Start->Run, entering "cmd" and clicking OK 

2 - Type the following command to enable 32bit mode: 

cscript %SYSTEMDRIVE%\inetpub\adminscripts\adsutil.vbs SET W3SVC/AppPools/Enable32bitAppOnWin64 1

3 - Type the following command to install the version of ASP.NET 2 (32bit) and to install the script maps at the IIS root and under: %SYSTEMROOT%\Microsoft.NET\Framework\v2.0.50727\aspnet_regiis.exe -i 

4 - Make sure that the status of ASP.NET version 2.0.50727 (32bit) is set to Allowed in the Web service extension list in IIS Manager. 

 Note: These instructions are provided by Microsoft. You should always make a backup before making any changes to any server or development machine.