I've been at a couple of sessions this week where this has come up (ISV Innovation Day and OzFox). Microsoft have a program whereby partners can create virtual images of their applications for users to download and evaluate inside a virtual machine. You can do all of the tricky configuration etc and let potential customers jump straight in.
From the web page:
VHD Test Drive Program
The Microsoft VHD Test Drive Program provides Microsoft’s partners a convenient and simplified process for creation of application images, facilitates its widespread distribution by making it available as a free download and enables accelerated evaluation and testing of these applications by customers. If you are Microsoft partner and would like to be able to distribute your applications in a VHD, you will have to sign the VHD redistribution agreement. To participate in this program, send an email to email@example.com and ask for a copy of the agreement to be signed and returned to Microsoft.