We are using ESX 3.5 update 2 and VC 2.5. We mainly use windows 2003 virtual machines, but now want to start installing windows 2008 OS and also exchange 2007. Are there any issues in running this OS version on this version of ESX or is it best to upgrade to VSPhere for better performance.
Any advice please.
Running the same environment you described and we have installed many Windows 2008 servers. Make sure you use the Windows 2008 Enterprise edition to take advantage of the virtual licensing rules. One anomaly we have seen related to performance is that the x64 version of Windows 2008 actually runs a little better in uniprocessor mode. In general I would say avoid x64 if you can as it may not play nicely with he available device drivers for your pre-existing environment.
Again - we are running almost all 64 bit so you can do it. You just may need to play with the number of processors depending on your physical host setup. We do not run Exchange so I can't give any particulars on that.