Ok, here are my settings on my machine.
I have an AMD Sempron 2 gig processor
2 gigs of DDR2 ram
4 gigs of ready boost
160 gig high speed HDD
And a Radeon 2600 pro video card with 512 megs of DDR2
I also have Vista Basic with the services tweaked a bit to free up some memory.



I have a 22" wide screen monitor with a native resolution of 1680X1050 but you will notice this is not what my setting are. I picked the one I have because it was a lower resolution and a bit wider which I liked the look of.
On the first screen the Global texture setting seems to effect how the planes look from the outside views mostly. At least as far as I can tell. Like I said in my above post, if you mostly fly from inside the plane this doesn't need to be set really high. I like to watch the plane in flight so I set it to where I get the best looks and the best performance. I can actually go a bit higher on some of my settings like the filtering and global texture but I can't tell a huge difference in looks so I just left them where they were to be on the safe side.
On the Scenery screen the fourth bar down on the left "Texture Resolution" is the one that has the biggest effect on how things look. This will effect how photo realistic the ground looks as you fly over it. Set it to where you get the best looks but the plane still flies smooth. Try several planes as well, because some of them react differently.
The two top bars on the right effect how many 3d building and trees you will see. The higher you set these the slower things will run. What mine is set to is the lowest setting you can have and still have buildings and trees show up.
For the traffic and weather just shut everything off. You can play a bit with the weather if you want. The detailed clouds look really cool if you can run them well.
Hope that helps a little.
Paul