Does service pack1 and 2 improves FSX?

[motoadve]

What does it do?
What changes or improvements?
No problems at all?

[tcco94]

Yes,

[Daube]

Expect display problems with the SP2 if you try to use planes that are in FS9 format. Usually those problems are just small transparency issues, that can be resolved by editing some textures, but sometimes it doesn't work at all.

[motoadve]

If I just want improvements and not the DX10 I just download SP1?
Will I be forced to use DX10 with SP2? Or is optional?

[BigTruck]

It's just a preview of DX10, and you can turn it off in the FSX settings menu.

[Daube]

If I just want improvements and not the DX10 I just download SP1?
Will I be forced to use DX10 with SP2? Or is optional?

As BigTruck just mentionned, the DX10 mode is purely optionnal. You can switch to DX9 or DX10 simply by checking/unchecking a setting and restarting the sim.
Flying FSX without the SPs is REALLY NOT recommended. Install at least the SP1. SP2 brings further corrections and optimisations, but also bring trouble with FS9 planes. If you don't use FS9 planes, go for the SP2. Else, you can try to stay in SP1, which will already bring a HUGE performance improvement compared to the retail version.

[Meck]

...maybe I should really switch to SP1 with my FSX!?!   :-/