My main PC is running Windows Vista Home and my laptop runs Windows Vista Ultimate. Basically I want to be able to have complete control over the desktop (Home Premium) PC while using the laptop.
If this is while both are at home, you can use remote desktop which is already built into windows. If it is accross firewalls the I suggest go the LOGMEIN route, as that will be the easiest.
VPN and Remote Desktop or VNC is best bet if you gonna need to copy files inbetween, don't think logmein enables you to transfer files. But as zamicro said, if its both on same network you can just use RDP.
You could also try Teamviewer also very easy to use.. You can use it for free on a non-commercial license, the speed is also not to bad, also you don't have to worry about opening ports and stuff, and you can set it so that only certain user id's can connect to your pc. http://www.teamviewer.com/index.aspx
I have found Radmin (short for Remote Administration) to be the fastest, but you have to buy it. http://www.radmin.com/
hope this helps..
UltraVNC or TightVNC is also not to bad, but I had some troubles when setting it up on my router..