You may have already done the following but could be worth a try...
- Click Start
- Settings
- Network and dialup connections
- Click "Make New Connect"
- Click Next
- Select "Accept incoming connections"

- Select a Modem if you don't have broadband else select nothing of a VPN.
- Select "Allow virtual private connections"
- Select an existing user of click "add" to add a new user with password.
The following is optional but recommended especially if you need to access more than one machine which are networked.
- Select "Internet Protocol (TCP/IP)

- Click "Properties"
- Select "Specify TCP/IP address"

- Input "From" I.E. 192.168.1.50
- Input "To" I.E. 192.168.1.100
- Click "OK"
- Click "Finish"
The steps are slightly different for Windows XP but basically the same.
If you PC is connected to the internet via a router instead of a modem then you will have to forward the following ports:-
1723 TCP
1701 UDP
500 TCP
These ports will need to be forward to the IP Address your machine.
Once this is done you will be able to either dial in or create a VPN connection.
Then you will be able to map a drive to any shared folders on the machine.
If you wish to control the machine you can do this by using program such as Radmin (Remote
administrator) , PCAnywhere or Remote Assistance in Windows XP.