I have to maintain ArcGIS Desktop v10 and v9.3 on different workstations in my workplace. I still need to use v9.3 to use extensions that are not yet available for v10. Right now I have to install only one version on each workstation, effectively nulling the concept of a floating license. Why can't I have both v9.3 and v10 installed on the same workstation and then have the License Server figure out which is which and check out one of my Desktop licenses in the appropriate version? I can do this right now with ERDAS Imagine, which has greatly improved its functionality as it evolved from v9.3 to v2010. On any desktop in my workspace I can run Imagine 2010 version for routine processing and the previous version for extensions and processes that are tailored for v9.3 and not yet modified for v2010; I can even open both versions at the same time, although it takes two licenses to do so. It frustrates me greatly that I cannot do the same with ArcGIS Desktop!