We have a MOSS 2007 Standard farm, running on 2 Web Front End (WFE) and 1 Indexing server all running on 64 bit Windows Server 2003 servers.
We need to upgrade our servers to Windows Server 2008, and wanted to know if you can run 1 WFE on Windows 2008 and 1 WFE on Windows 2003, while we are in the process of upgrading our individual servers.
I've had a lot of experience with MOSS, but haven't actually tried this. However, I don't see any reason why it wouldn't work; the MOSS instances should still 'talk' to each other the same way, regardless of the underlying Windows operating system.
I have ran an 64-bit Windows 2003 indexing server and 4 32-bit Windows 2003 WFEs with no issue.
If you have a test environment, I'd recommend trying it there first.
Ok, finally was able to get my network team to set me up a VM so that I could test running MOSS 2007 in a mixed OS environment. I can confirm that for MOSS 2007 you can run different servers with different operating systems. I have one WFE running 2003 and one running 2008. There are no compatibility issues.