1) If I choose to use an existing ESX host for evaluating Lab Manager, what is the impact to existing VM's and the ESX host during the course of the eval?
I would advise a seperate ESX HOST, as many of the Virtual Center functions are not compatible with Lab Mananger - IE DO NOT PUT the ESX host into a cluster
Does the LabManager agent install (or uninstall) require a eboot of the ESX host?
No reboot required
2) I already have 1 VMkernel Port on VSwitch 0 for NFS. Do I need to create another? Should it be in another Vswitch?
You need a virtual machine vSwitch for the LMNetworks000 etc... remember this is for networking not storage so the NFS vSwitch is for storage over IP
3) Will I get a satisfactory trial using a host with VM's already in place, or do I need a fresh install?
Use a clean install of a host with no vm's on it. remember you might find loads of vms appearing so you dont want to interfere with Virtual Center and whats currenty managed.
This comes from the release notes of ESX 3.5, VC 2.5. As I understand the note, it states that you can mix VirtualCenter and Lab Manager on same ESX host, and that it is supported now. is it right or am I missing something?.
NEW: Lab Manager 2.5.2 Support—ESX Server 3 version 3.5 hosts can be used with VMware Lab Manager 2.5.2. ESX Server 3.0.x hosts managed by VirtualCenter 2.5 are also supported in Lab Manager 2.5.2. However, hosts used in Lab Manager 2.5.2 must be of the same type.
Lab Manager 2.x hosts can be registered with VC. However, as noted, DRS/HA/VMotion are not supported. VC can be used as a place to get information about your LM hosts, reporting, or host maintenance. VC and LM 2.x do not communicate with eachother, so anything beyond that would cause issues (such as making changes to the VM through VC rather than LM or messing with the vSwitches)
I hope that clears things up.