|I assume you need to install to a computer that does not have an optical drive then? If so, it probably is a netbook which will have a SATA hard drive. The files on the flash drive will need to include SATA controller drivers. WinXP does not have those files so you will need to slipstream them into your original WinXP files.|
You need to supply more information to get better advice.
What is the brand and full model of the computer you want to install WinXP on?
What service pack is included on the WinXP CD you have?