I'm assuming your dad remotes into his other computer at work, and you'd like him to be able to remote into that machine via the Internet. I'm also assuming your dad's second computer is in that same office and he's not using the Internet to access it, just the LAN.
Simplest thing to do is open up port 3389 on your dad's firewall at work, and forward incoming TCP traffic on that port to the internal IP address of your dad's other computer. However, this is bad for security (anyone can try to remote in and try to guess passwords, etc.) It's possible to set up the office router to allow this and do a bunch of other things, but I'm assuming your dad is sharing the office with others and won't have the authority to change network or firewall configuration at will without going through someone else.
Probably the easiest and best thing to do, unless your dad wants to deal with the office's IT department, is to sign up for something that uses an intermediary system. I believe either LogMeIn or PCAnywhere is going to do what you need.
Since your dad's second computer at the office likely can't accept arbitrary incoming connections from the Internet, what needs to happen is that your dad's second computer connects to an intermediary service. This works behind NAT and firewalls because that computer is initiating the connection, which is allowed. Then, when your dad wants to connect to that computer, he logs into the intermediary service, which then uses the existing connection your dad's computer started to actually initiate and setup the session.
1I'm sure you're very proud of him, but the fact that your dad is an accountant is irrelevant. The fact that he works in a law firm, again, that's so wonderful, send my congratulations to his mother, but it's irrelevant. Some like logmein , others like teamviewer, but I don't think you'd get no lag whatever the solution. You could ask which solution has least lag., maybe not much difference between the two, but I don't know. He may be more comfortable with one than the other. But make sure you're comfortable with it have tested it prior to providing the solution to him. – barlop – 2011-05-15T18:13:05.360
Bear in mind that the boss may not appreciate it. So you could let your dad have the software installed in a laptop he brings in, and make sure he takes the laptop home with him so Mr tech doesn't come in after hours and see it and mention it! But Mr Tech might notice anyway if he comes in and has a look at the laptop to get it on the network or to fix something else. Your dad should get away with it though I suppose.. being not highly technical, with computers and having a computer-wiz son that set it up. – barlop – 2011-05-15T18:16:44.187
You're not clear on which computer he's connecting to. If he's connecting out then it shouldn't matter, if he's connecting in then Mr Tech might not be so pleased, and Mr Boss might not. – barlop – 2011-05-15T18:19:30.907
possible duplicate of Remote connection to a PC over internet
– Kez – 2011-05-15T18:27:11.557The fact that he's your dad is irrelevant too. Nobody here is going to be meeting the family. – barlop – 2011-05-15T18:32:59.803
3Did you have a bad day @barlop? – wullxz – 2011-05-16T06:09:24.503
@wullxz it's called constructive criticism – barlop – 2011-05-16T11:39:54.157
yeah, your constructive ctiticism made my morning :D – wullxz – 2011-05-16T12:40:10.310
4@barlop constructive criticism is when you edit and remove the irrelevant posts and mention a comment about it, not ranting about it in 600+ characters of comments. – Sathyajith Bhat – 2011-05-17T04:02:46.537
@Sathya 3 sentences spanning 2 comments. 2 sentences in the first comment, beginning it. 1 sentence in a latter comment. Total of 3 sentences totalling to <300 characters including spaces. Consider that a large comment is about 600 char. So mine amounted to half the size of one. Just 3 sentences. – barlop – 2011-05-17T12:26:02.347
way to miss the point, @Barlop. – Sathyajith Bhat – 2011-05-17T13:55:09.647