It won't matter what order you have the monitors, as long as they're the same resolution. You will, however, need an adapter, as Eyefinity will only allow for 2 "legacy" connections. You'll need to pick up a Displayport to DVI active adapter. I picked up mine on eBay for about $25. Try not to use the VGA connection at all. My current setup is DVI, HDMI, and then my DisplayPort to DVI connection.
EDIT: Here's the adapter you'll need, since your card of choice doesn't happen to provide one.
heya. I'm having weird problem here as well and was wondering if someone could help me.
I've got 3 acer s273hl.
Here are current connection CARD->adapter(s)->monitor
1. DVI -> dvi to vga adapter -> vga cable to vga in monitor
2. HDMI -> hdmi cable to monitor
3. mini display port -> active mini display port to DVI adapter -> DVI to HDMI adapter -> HDMI cable to monitor
Now I couldn't attach DVI to vga adapter and then connect VGA to VGA in monitor as in number 1 case, as somehow DVI to VGA adapters can't fit DVI on active adapter!
Ok now the thing is that I've got all 3 monitors working but from time to time my monitor that is connected over minidisplay port is blanking on and off.
Less in windows environment but really frequently in games or when 3d software window is on it.