Hi,
Is the issue that you want to be able to access your clients computer directly, so that your client doesnt need to do anything himself?
If so, a cool solution would be to ask your client to give you a login account on his computer (a username and password) and to enable remote login (in sharing preferences) and to leave his computer running. (this is assuming that your client is willing to give you such access and that it creates no security problem for them)
you would then be able to access the clients computer (the remote computer) directly via secure shell (ssh) using the terminal application in the utilities folder.
you would type:
ssh username@123.45.67.8
(obviously using the real username and ip address). then after entering your password you could then have a full secure (encrypted) unix session (including transfering files from the remote computer).
(the above assumes the remote computer is not behind a router--if it is, you would have to set up port forwarding on the router to send traffic on port 22 (ssh) to the remote computer.
if you prefer a graphical interface, you could set up a VNC server on your clients computer (like OSXvnc) and a VNC client on your own computer (like Chicken of the VNC). set the ip address on Chicken of the VNC to 127.0.0.1 and assuming the remote computers monitor is 0 (equivalent to port 5900), you would use terminal to set up a secure shell with local forwarding to send your local port 5900 to the clients computer. it would look like this:
ssh username@123.45.67.8 -L5900:127.0.0.1:5900
after entering your password, you would be able to start chicken of the VNC and the remote computer desktop will appear and be fully functional with your mouse and keyboard.
hope that helps,
Rich