Sony site to see if there are XP drivers available for your laptop. If not, you will need to track down drivers from various mfrs websites for things like video and wifi.
Good Point, I personally made this mistake with an install of XP, nothing worked Wifi USB Ports Ethernet, i had no connectivity to even download updates.
So I also suggest this and make sure you have a spare CD in case the only thing thats works is the disk drive.
full version XP, boot your laptop from it, and follow the prompts to install XP. When it gets to the hard drive options portion of the process make sure you delete all existing partitions before installing.
You will have to do a Clean Install, and windows 7 wont let you install XP using its application (incase you already tried to through the OS).
I would say click to format the partition Windows 7 on before installing, this way you know everything is gone.
If you want to keep all your data, download easeus. Its really good partition manager which will allow you to create a partition big enough for you to put your files on.
Also, if you downgrading to XP due to compatibility problems with Win 7,
Right click on the application, Properties, Compatibility, Run this program in compatibility mode for: Windows XP.
Or Download Windows Virtual PC and XP, If you have ultimate its free.
Windows Virtual PC: Home Page