First off, you don't need a translation program such as MacLinkPlus. That's the beauty of Mac OS X.
Also, since Mac OS X is standards based, you already have TCP/IP turned on. Since this is a PC, you don't need to turn on AppleTalk.
When I connect to another Mac over the internet, I used SSH through the terminal, but that solution may not be idea for you.
The previous poster is right about just finding the IP address. I think that if you get on the phone with the client and have him go to Start>Run>command and then type ipconfig and then have him give you the IP address of the adapter that connects him to the internet and then you go to your mac and hit command+k and then type smb://hisnumber and hit connect you should get a connection box. Now, you will need to access to his computer.
So, you can have him set you up an account on his computer (Control Panel>Users in Windows pre XP and Control Panel>User Accounts in XP) and then right click his HD and go to sharing and set that up giving you full access. Then you type in the user name and pass that he gave you from his PC and it should connect.
However... if you are connected to a LAN, and your Mac gives that connection priority, it may give you a message saying you cannot connect. Then you will need to unplug/turn off those network connections.
Since the PC isn't set up, it might take some work on the part of your client. PCs are just that way. It's easy on the Mac though. Sorry if I've made the Mac side sound hard... it's not at all. Trust me. And post again if you need more help.