My BIOS does not have a memory remapping feature
Sort of begs the question of why have 6 GB installed. Looking at the specs for that motherboard (which is from Acer),

Acer Support: Aspire M1100 Specifications

it only supports up to 4 GB to begin with (no reason other than Acer wanted it that way as the AMD 690 chipset can support up to 16 GB), so not only is 2 GB not available to Windows, it isn't doing anything other than filling the empty ram slots.

You're also running a chipset that has no official Windows 7 support beyond whatever Windows will install for default drivers. The best you're going to get for the chipset is the last Vista driver (I know it says display driver, but it also includes the chipset),

ATI Catalyst

Same goes for the onboard NIC, of which Acer doesn't have a Windows 7 driver for. I did find this Asus board that has the same Marvell adapter on it and Asus does have a 64 bit Windows 7 driver for it,

ASUSTeK Computer Inc. -Support- Drivers and Download P5E3 Premium/WiFi-AP@n

Just select Windows 7 64 bit from the dropdown and grab the LAN driver, it should work with yours.

I'd start with leaving it at 4 GB as the extra 2 GB can't be used anyway. Then start with trying the Vista chipset driver as well as the Windows 7 NIC driver and see how it goes.