The simplest/quickest approach is to simply make the Windows XP the
default start-up OS. To do this, in My Computer, pick Properties, Tab:
Advanced, Section: Startup and Recovery, Button: Settings. System
startup section at top of dialog box.
To remove Linux, check with the setup documentation that comes with the
Linux Distribution. Most of the distributions explain the process.
I use the 3rd party product Partition Manager to remove OS's and
repartition disks to reclaim the space. The process to do so is fully
described in documentation for that Partition Manager.
Whatever you do when removing the Linux partitions., ensure you are
familiar with what you are doing so that yo don't inadvertently delete
the XP OS.
Hope this is useful to you. Let us know.
rms