Just sounds like you are making work for yourselves. Test both ends of the cable and record the worst reading.
How can it be 2 devices when it is one physical item?
Depends on your setup. I've got a SAN and 3 ESxi servers. I can just take vmotion the vm's off one and update it. Upgrading vcentre can be done anytime. It doesn't affect the running of the esx servers.
Update vcentre first. You can then use update manager to update your hosts.
Have a look at:-
http://www.vmware.com/pdf/vsphere4/r40_u1/vsp_40_u1_upgrade_guide.pdf
Andy
You can upgrade VC 3.5 direct to 4.0u1.
I've just upgraded to u1 from 4.0 with no downtime. (Well almost, you have to restart the vm's after a vmtools upgrade)
@Theblacksheep. Are you running View 4? Are you using thin clients?
Andy
Have you got a computer account in AD for the smoothwall box?
Are the dns entries correct? Needs both the forward and reserve lookup zones to be correct.