Virtualization

That would probably depend on whether you are going to stream to a Terminal Server or not. [:)]

Read this link:
http://www.microsoft.com/systemcenter/softgrid/evaluation/softgrid-ts.mspx

Streaming to Windows XP Pro should not require terminal server compatibility.

That would probably depend on whether you are going to stream to a Terminal Server or not

To a point - some apps check for TS environment and refuse to run if they detect one. That you may not be able to get around.
For (poorly written) apps that store user-specific data in a static location (e.g. off the C:\, or in %ProgramFiles%), you should be able to get around the concurrency requirement if you sequence properly.

Some of the TS-unlikely apps that pop to my head are VPN clients of different flavors...

SoftGrid / App-V or any application virtualization can usually help applications that are not TS compatible run on a terminal server by isolating files, registry and COM objects to be per-user but as mentioned in this thread if the application checks to see if the system is a terminal server you'll have some challenges to overcome.