Gobinatty,
Using your IP Softphone over a VPN link shouldn't be much a of a problem if your able to establish a fast VPN link to your office.
So you might ask 'How will this be done?"
It's quite simple actually - you can either purchase dedicated VPN equipment which usually resides at the premises we want to access (in your case - your office) and then load a VPN client on our laptop/pc which will allow the VPN tunnel to be created between the two end points.
Once the connectivity part is complete, its a matter of configuring your softphone to enable the service over this new link.
Because you haven't mentioned anything in regards to the VPN, are you planning to create one, have one already installed or looking around for VPN solutions?
You can also setup a VPN using Windows 2000/2003 as a VPN server and terminate your XP Home laptop to it.
We'll need more information from you if you require us to be more precise with our answers.
Cheers mate,
Cheers,
