This is a good setup for using VirtualBox to host multiple Windows XP's:
Install a Windows XP as guest and select the host-only network adapter. That way you can connect from your Windows 7 host to the Windows XP guest. In the XP guest create a static ip-address, for example 192.168.56.120. That way, you will always have the same ip-address to connect to. Ofcourse check the firewall settings, and do not use http://
localhost to test a website on the guest, use the full guest ip-address like http://192.168.56.120.
But with the host-only adapter, you do
not have internet in your XP guest. There is an easy way around that. Simple install a second network adapter in VirtualBox. That must be a 'NAT' adapter.
This way, you can connect to your Windows XP guest and have internet in the guest. Maybe some ask why I do not use the bridged adapter. That's because the bridge cannot connect to the guest when you disconnect your adapter from internet.
Please notice that VirtualBox "Shared Folders" are the fastest way to share data between the host and the guest operating system. (click a virtual machine and right-click for settings/shared folders)