Dual monitor problems - FSX

Hi,

I know it's a pretty beaten up topic but after reading about it for days I couldn't make heads or tails.

My system is mediocre: Core2Duo and a GT 520. Yet I'm happy with it and can get 50+ FPS with default aircraft and very high settings (AI traffic always off because I fly 99% online). FPS goes down to some 20 with complex aircraft and/or busy areas but I'm happy with that as well. I can see it's the CPU bottlenecking since one core is always maxed while the GPU is at ~50% capacity. When it gets hairy (bad weather etc.) the GPU goes up to some 70 or 80% with no FPS impact. So life is good.

I have two monitors and the way I've been playing is FSX windowed on the main (24") with FSInn and other stuff like charts and flight plan on the second screen (17"). Works like a charm and no performance impact whatsoever over running with only 1 monitor.

However, I started a few days ago fiddling with having 2D panel windows on the other monitor (like a FMC). At some point I even hooked a third monitor over the network, thinking about getting the overhead panel there. The networked monitor works fine with every software except FSX.

If I'm running in windowed mode: I undock any window (say FMC) and immediately lose a ton of performance. Like, from 20FPS (complex aircraft, busy area) it drops to 13. If I undock another one (say overhead), it immediately drops to 8FPS or less. Unplayable. (on a side note, is it possible to get rid of the blue bar and frame out of an undocked window?).

If I'm running in full screen, the second monitor is always black. Even if I drag a FS window to that monitor, it's still black. Nothing ever happens. I'd be very happy running both monitors full screen and then having my charts etc. on a separate laptop. I don't really need to alt-tab for anything during flight so full screen would suit my needs if it worked.

Sorry to post asking help on a beaten subject, but like said I've been reading and searching it for days. I've seen people can use multiple monitors when on full screen but I can't see what I'm doing wrong/different.

Many thanks.

edit: just already addressing first questions. Win XP 32 bit. Latest video drivers. FSX with SP2 (no acceleration). I've read and ran every tweak I could find on the web over the last few months, although most of them didn't work. Even the mighty highmem=1 causes problems on my system, so the fsx.cfg is pretty much the default.