An interesting followup problem to the original post:
As you may have surmised from my original post above (and followups), I've managed to get us through several rocky server upgrades (most recently to Windows Server 2008 R2 and Exchange 2010, as far as I know, IT is not too forthcoming with info, and I am the only Mac guy to deal with this) and get everyone working on Macs at home functioning ok up until recently. The VPN works fine, and all of us have been able to use RDC 2.1 to log on to our work Win machines.
Until a couple of weeks ago. All of a sudden, several of us - though not all of us - can't access our Dells from the Macs, receiving the "Remote Desktop Connection cannot verify the identity of the computer..." message. Nothing changed on the Mac end for any of us, as far as I know (no major system updates or anything), and since then we've tried several different configurations of user names, passwords, domains, etc. but none of them succeed.
The only lead I have right now is that one of the people who can still connect is pre-Snow Leopard, and the two of us who can't ARE on Snow Leopard - same version of RDC, same VPN, etc. But she can connect and we can't. I'm polling the other home Mac users now to see if that correlation holds. (Apparently that isn't the problem, another user just chimed in).
Now, I would expect that checking the "Always connect, even if authentication fails" option in the Prefs would fix that; this is what MicroSoft recommends doing if you have this issue in various situations. But it doesn't work. MOST of us cannot connect, and I can't find any rational explanation why not, or why not all of us are affected, or why that option won't let us bypass the issue.
So my new question is twofold:
1) Why doesn't that option allow RDC to connect regardless of the identity of the computer? I'd think if it couldn't actually find the computer it would tell me that - the fact that I get the "Can't verify the identity" message indicates to me that it SEES the computer, but won't connect. Is this a known issue with Mac RDC 2.1?
2) Are there any known issues or obvious things from a Windows desktop or server side, when interacting with Snow Leopard or Mac RDC 2.1, that I know should know, or that might be causing this, either the connection issue or the non-working "always connect" option?
Any help would be AMAZINGLY useful - thanks in advance for any advice!