Nick, you are right. I was using a 32-bit Eclipse with a 64-bit JDK 7 in a Windows 7. I tried now with a 64-bit Eclipse and I was able to install Jboss Tools.
I was using a 32-bit Eclipse because the problem originated in another machine with a 32-bit Eclipse, 32-bit JDK 7 and Windows XP. Do you know if it´s possible to install JBoss Tools in a 32-bit Eclipse even with a 32-bit JDK? Anyways, tomorrow I will double check this other machine configuration (I don´t have it with me now).
thank you