That is a very old patch for windows xp that supports the newer encryption.
You don't have a lot of options. If you control the router you could temporarily change the encryption back to wep or none. Or you could use a cable and cable it to a router.
If neither of those is a option you are going to have to download the patch with another computer and then use a USB drive or DVD to move it between the machines. If you dig around on microsofts site you will find the files used for offline patching.
You might as well download the complete sp3 patch since there are other security patches you want also.