Windows vista basic home edition problems?

i have a oshiba laptop that is running windows vista basic home edition, i know there are about 3 viruses on it. my problem is that i can't open wordpad or anything similar to it. when i try to download something (microsoft security essentials) it won't actually download it. the save dialogue box comes up and everything and asks where i want it and save or run, wll when i click either save or run it just closes out of it. so i can't download any security software or anything to get the viruses off... please inform me on how i can get around this so i can get the viruses off my girlfriends computer