You can do this for free.
1. Go to
No-IP - Dynamic DNS, Static DNS for Your Dynamic IP and do the free dynamic dns service.
2. Install ultraVNC (or any other free VNC servers out there)
3. Get the android-vnc-viewer app from the market place.
4. Log into your computer using the web address that you received from no-ip.info.
Edit: with the no-ip service you can even run a web server or ftp server and log into them from anywhere in the world using your browser or FTP client. (I use AndFTP for my ftp client and it works great.)