Not too difficult, here are a few tips to make sure that your experience is flawless.

When configuring the virtual machine, make sure that you

• enable APIC and ACPI in Settings –> System.
• create a fixed sized harddisk to improve disk I/O speeds.

After installing Windows XP, make sure that you

• download the driver for the Intel Pro 1000 network adapater and change the default adapter from PCNet to Intel Pro 1000 in Settings –> Network. For me, this improved network access speed and reduced DNS lookup delays.
• install VirtualBox Guest Editions which enables seamless mouse integration and experimental Direct3D support by mounting the Guest Editions ISO.
• if, in the event that Windows Update fails to work, register the Wups2.dll as outlined in the Microsoft Knowledge Base <http://support.microsoft.com/kb/943144>

I extend my thanks to the VirtualBox team for making this so effortless. By the way, anything between 5G – 10G is a good size for your virtual harddisc.