Using your card on Windows XP
Warning Windows is a non-free operating system! This means it takes away your freedoms to use, study, share and improve the software.
Presumed you already have a smart card reader. You need also to install GnuPG for Windows. GnuPG for Windows can be downloaded from here: http://www.gpg4win.org/download.html
Go to prompt mode (execute cmd.exe); gpg --help will give you the list of commands and options available.
In order to modify the content of your card, use: gpg --card-edit
More useful information on GnuPG, which is to a very large extent applicable for Win machines, can be found here: http://www.gnupg.org/howtos/card-howto/en/smartcard-howto-single.html#id2456468