The planning steps are incredibly important for a successful configuration of any VMware implementation, regardless of shape and size. One specific area you should consider while planning is supported guest operating system configuration limitations.
VMware frequently updates the Guest Operating System Installation Guide (GOSIG), an online book that gives specific information for VMware ESX Server, VMware GSX Server, VMware Server, VMware ACE, VMware Workstation and VMware Fusion guest operating systems. This guide gives very specific configuration matrices for the VMware product and the guest OSes that can be run within the product. Further, there are very handy known issues sections for each guest OS.
Supported VMware Server 2.0 configurations
A specific example that I have found this guide helpful in regards to VMware Server 2.0. According to the GOSIG resource, Windows Server 2003 is only a supported configuration on VMware Server 2.0 with Service Pack 1, Service Pack 2 or the R2 features added to Windows Server 2003. VMware ESX, however, has a fully supported configuration for Windows Server 2003, including the base release without any Service Packs or the R2 features, in all versions from 2.0 through 3.5 Update 3.
Supported Windows Server 2008 configurations
Some configurations are more obvious, such as running Windows Server 2008 as a guest operating system on a hypervisor that predates the release of the guest OS. In the GOSIG guide, Windows Server 2008 64-bit guest OSes are supported only on more current products. Some platforms, such as VMware GSX server and VMware ESX Server 2.x and 3.0x are not a supported configuration for this guest OS. Even with all of this information, and the officially supported configurations – you may find that certain situations are successful even though they are not listed in the GOSIG documentation. A better practice would be to match the hypervisors with the supported configurations in regards to the guest OSes, and this may mean standing up different versions of VMware products to cover the full range of OSes that are required in your environment.