I am the tech support person for our family. For my wife's grandmother, I installed a Windows Home Server in her house. One of the features of the Windows Home server is that it is a proxy to allow you to RDP into the other computers on the network. The problem is that this only works for the computers that have the RDP server enabled. (i.e. Windows Vista Ultimate...)
Windows Live Mesh has a similar feature, but it doesn't have the requirement that the windows installations has its RDP server enabled. Live Mesh's implementation requires that the Live Mesh client is installed on the computers that you want to access, and the computers that you want to do use to access them. Once you have the software installed, you need to log into Microsoft's live server on each computer. Then from any computer signed into a Live Mesh account, you can connect to any other computer also signed into that account.
The problem is that this doesn't really work well with multiple accounts. For example, I have a Live Mesh account, and normally am logged into it when I log into my Windows account. When I want to help out family, I need to log out of my account and then log into their account. Ideally, Microsoft would add the ability for a Live account holder to be able to grant access to another Live account for a particular computer.