As explained by @morpheus682 in his review :
"Sadly it seems that somewhen they patched a as of now unfixed bug in, that prevents random maps from becoming bigger than 512x512 fields; the steam version has threads for it.

So to get up to 2048x2048 you either need to play one of the included maps or somehow get a random map from somewhere, which i, having the CDs (if i ever find them on the attic) might be able to, but otherwise may not be easy considering the games age. "

So I was wondering, has anyone found a way to generate big maps by any chances ?