You probably mean two gigs, not two megs. :-)
IMO, two gigs is too low for V7 but if the scene is really that simple, then it may not be the cause. Do you have the latest build of V7? I remember that in the early releases the program choked with large groups of objects. I also experienced a sluggish behavior with some of Walli's grasses (from C3D). I don't know what was in that object that made it like that but it happened. Maybe you could try deleting the objects one by one until you find the culprit.

Regarding Windows7, Microsoft said that if you buy Vista after June 26th (if my memory serves me right, please double check the date) you're entitled to a free upgrade to Windows7 when it comes out (which should be before Christmas). Every expert, every review says that Windows7 is great.