If you're running GuestCustomization settings, you can set the primary IP easily enough.
If you need more advanced IP address configuration, you can use the GuestOperationsManager or VIX API (vSphere 5 vs vSphere 2.5/4) to run in-guestOS programs to set the IP information. For example, you can use Windows WMI or netconfig to do CLI network configuration. Similary, you can run or modify Linux text files to the same effect.
Bear in mind, the VIX/GuestOps APIs do not use networking to talk to the guest. They speak to the HostSystem that is currently the parent for the VM, which then uses an internal channel through the VMware Guest Tools (so Tools must be installed and running). It's an excellent solution for IP management, since you can still connect in the event a GuestOS network is misconfigured and inaccessible through standard IP networking.