Here you go: http://lmgtfy.com/?q=arm+virtualization

There are primarily two things that are required for running usable, responsive virtual machines: CPU power and RAM
Unfortunately, the N900 is sorely lacking in both.
Yes, the CPU can be overclocked (in some), but that only goes so far.
The RAM cannot be upgraded so you are stuck at 256MB, no matter what you do.
Virtual memory is of little use here, since it is thousands of times slower than RAM... the N900 already suffers greatly when using only a couple hundred megabytes of swap (which it does only running 1 OS).

The N9 would be a much better target due to it having 4x the RAM of the N900.