According to the license under which VDMSound was released, you already have permission to include it in your installer as long as you:
- include a copy of the version of the GPL under which VDMSound was released (VDMSound should include a copy of this itself, so you just have to not take it out)
- state that VDMSound is licensed under the GPL
- give credit to Vlad for VDMSound
- link to the VDMSound site so people can get the source if they're interested (or maybe keep a copy on your own site in case the official one goes down)
Actually I'm not sure that all of that is necessary, but it will definitely cover the bases.