Someone mentioned Windows, so I figured I'd say that. Anyone can figure out easily enough that Linux is very easily installed via USB.
And I've very rarely seen a bug when running 32-bit applications on a 64-bit Operating System, and even then, it's usually due to a bug or poor coding. Theoretically speaking, there should be no significant decrease in performance when running a 32-bit application on a 64-bit architecture. Actually, in a good portion of cases, the 32-bit application runs better under the 64-bit architecture, with the 64-bit version of the software running even faster.
So even when you have less-than four gigabytes of RAM, it's still very much worth it to run a 64-bit architecture, with a 64-bit operating system.