When you install Acrylic along with VWD Beta 2 and add Acrylic xpr file to the Web site, you will see that VWD, in fact, knows about Acrylic and displays correspondent icon:

You probably won't be using original XPR file and instead will be using exported raster image, such as PNG or JPEG. However, you may want to track the original XPR file in case you need to update it and regenerate rasterized images. In order do establish link between file types, create and run asmall registry script:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\8.0\Projects\{E24C65DC-7377-472b-9ABA-BC803B73C61A}\RelatedFiles\.png]
"RelationType"=dword:00000001

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\VisualStudio\8.0\Projects\{E24C65DC-7377-472b-9ABA-BC803B73C61A}\RelatedFiles\.png\.xpr]

It will add association between XPR and PNG file to the VWD project system. When you are done, restart VWD and you should see the following in the Solution Explorer:

Now XPR file is associated with the PNG file as CS/VB files are associated with their correspondent Web Form files. You will lose the Acrylic icon though since linked files share the same icon.