Cómo saber si mi puedo instalar Ubuntu 64 bits?

No es nuevo este tema y no voy a explicar las diferencias entre 32-bit  y 64-bit.

Con la nueva funcionalidad multiarquitectura en Ubuntu 11.10, se me dio por probar finalmente Ubuntu 64-bit.

Ubuntu 11.10 provides "multiarch" support for installing 32-bit library and application packages on 64-bit systems. For all amd64 installs and upgrades, select 32-bit software (like Skype and Flash), will now be installable directly using the same 32-bit packages that are used on i386 installations. You are not required to install the ia32-libs compatibility package. For users, this change means that the 32-bit libraries will always be available at the same time as their 64-bit counterparts, even in the case of security updates, and users will only need to install those 32-bit libraries required by the user's application(s).

¿Cómo saber si mi computadora es compatible con 64-bit?
Abrir una Terminal y escribir:

 grep --color=always -iw lm /proc/cpuinfo

Si el comando devuelve lm (LongMode) cómo uno de los flags, entonces tu procesador es compatible con 64-bit.