Workflow Foundation vs. BizTalk
The answer really depends upon what they plan to use BizTalk for. If their primary use of BizTalk is to design simple workflows / orchestrations, then they might get that kind of functionality for free in .NET 3.0 Windows Workflow Foundation (WWF).
WWF is however just a framework, so-to-speak, not a complete product such as BizTalk. WWF, for example, does not have features such as pipelines or adapters, and there are no administration tools such as HAT or BAM that come with it. These functionalities can definitely be custom developed as required, but for large solutions (e.g. B2B or integration of desperate systems) it might be best to just invest in BizTalk and leverage all the tried and tested tools and technologies that come with it out of the box. For other solutions such as a program’s internal workflow, WWF will prove to be an invaluable tool.