I would like to create a large natural landscape with animations(waterfall, river, ocean, wind moving objects). I am a just wondering if the polygon count of a epic landscape is feasible in blender. I dont know how a plane or ANT terrain object subdivided many times for detail would behave in the scene window or even if the entire object would need high subdivision but I do know I would need high subdivision at many points on the objects since I would be sculpting detailed cliffs and mountains(not simple smooth falloffs created with proportional editing) and I also know a cube I created with 100,000 verts rotated ok in the Scene window(Wireframe) but the next subdiv(400,000 verts) barely moved.
To operate with high polycounts you should make sure that your scene preview subsurface levels are as low as possible when you aren't working on them(so split up your scene into smaller sections). Also, you can put sections you aren't working on in wireframe view(this does help). Splitting stuff up into different scenes also helps.
When I do high polycount scenes I work on them section by section on different layers then put them all together but only leave the center in solid mode.
So yes, Blender can work with high polycounts on a lower machine but you'll probably have to jump through some hoops to do it.