Not sure why Trend Micro would cause any problems with connectivity unless you used their firewall. Simply don't use it. For the record, to compare apples and oranges, I used Trend Micro's Client Server Messaging Security for SMB. I am not bragging, but the server software runs around $650, so it is hard to compare.
Paul, there are many solutions for your problem, the cheapest of which would be RDP (Remote Desktop). But, that's much easier if one end is static. Static does cost money monthly. VPNs be done with dynamic end points, but they are usually done with one side having a static IP. VPNs are a nice way for two offices to have a fairly constant connection, but you will still need software such as Citrix to be able to access the desktop.
I have said this before at least five times, and I couldn't agree with Brian more. I just don't understand why you don't use LogMeIn (the free version). It can be set up in under five minutes, and it will do everything you want it to do.
hth
