First thing, the documentation on VI Toolkit :

http://communities.vmware.com/docs/DOC-4210

If you want to connect to more than one virtual center at the same time, here the starting code :

Be carrefull, the command GET-VM $VCS will not return the same values than GET-VM.
If you use GET-VM, you will receive the VM List only for the Virtucal Center that you connect last. If you want the get all the VM of your different virutal centers, you absolutly need to add the parameter -server $vcs to you command. In a general way, don’t forget to add -server $vcs to every command than you use with the VI Toolkit.

1. Open registry editor, locate HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\COM3, and then delete this key.
2. From the Start menu, point to Settings, click Control Panel, and then click Add/Remove Programs.
3. Click Add/Remove Windows Components.
4. Proceed through the wizard, and accept all of the defaults. (COM is reconfigured)
5. Restart the computer.

After that, reinstallation of the tools :

1. Create a directory (c:\vmtools)
2. Mount the VMware Tools CD
3. Copy VMware Tools.msi to the directory you created
4. Copied the VCBRequested.dll and VCBSnapshotProvider.dll from vmware tools cd\program files\VMware\VMware Tools\Drivers\vss\Win2003 to the directory your created
5. Cancel the VMware tools installation that has started itself
6. Using 7Zip ( http://www.7zip.org/) I extracted the VMware Tools.msi file (rightclick on the MSI, Open Context Menu for 7-Zip, selected Extract to VMware Tools
7. Now within the c:\vmtools directory you will have VMware Tools Folder
8. Within the VMware Tools Folder there will be a file Binary.ComReg.exe, take a copy of this a place it somewhere within the %path% – say c:\windows\ and rename it ComReg.exe
9. Now create the following path c:\program files\VMware\VMware Tools\Drivers\vss
10. Copy both the VCBRequested.dll and VCBSnapshotProvider.dll from the folder you created in step one to the path you created at step 8
11. Now run the following command :

     comreg.exe -register "c:\Program Files\VMware\VMware Tools\Drivers\vss\VCBSnapshotProvider.dll" "VMware Snapshot Provider" "vmvss" "VMware Snapshot Provider"

12. Finally, run the Vmware Tools install process, and this time it should work

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It is possible that your VC is v2.5, our Virtual Center SMP does not support that version by default, but we have developed a patch in order to provide support for this version. Just follow these steps in order to apply it:

1. Download the patch from: http://download.jalasoft.com/pub/patches/JS0176TD/Patch20080711.zip
2. Go to the server where Xian was deployed and stop the ‘Jalasoft Xian Network Manager’ service.
3. Go to the following folder: ‘[program files]\Jalasoft\Xian Network Manager Io\Plugins\Jalasoft.Xian.Plugin.VMwareVirtualCenter\resources\’
4. Replace the ‘Jalasoft.Xian.Plugin.VMwareVirtualCenter.config.xml’ file with the recently downloaded.
5. Start the ‘Jalasoft Xian Network Manager Server’ service.
6. Open the Xian console and try discovering your virtual centers. Please note that discovering a VC could take several time (depending on the amount of ESX servers hosted in it), so it is recommended to increase the ‘timeout’ and  ‘maximum number of retries’ parameters on the execution of the discovery rule.