Well, obviously these won't be the lowest in that literal sense (after all, you could presumably reduce the resolution to the point of which you can't see anything anymore), but practically reduced, try tweaking the following INI lines:
ScreenHeight=600
ScreenWidth=800
Lower resolutions = smaller window size = less work. Resolution is the easiest thing to change and would have some of the biggest impact, but if decreased too much, you may be unable to see what's even going on.
Shadows=Disabled
Turning off shadows gives a big performance boost.
Textures3D=0
Disabling 3D textures makes water instantly hideous, but can improve performance slightly, and really old video cards won't support it.
TilesetParticles=0
UnitParticles=0
Particles are very heavy on your computer. Sure, a couple of mages is manageable, but when we got an army of units that generate particles just by standing there, that's a fair bit of work on your computer. Disabling them completely misses out on a lot of eye candy, but reduces strain nicely. On a side note, some units (off the top of my head, the ghost-workers from the Undead mod) would not be the same at all without unit particle systems.
FogOfWarSmoothingFrameSkip=5
Higher numbers would mean the Fog of War clears less smoothly, but also slightly less work when doing so.
Windowed=false
I'm told that fullscreen mode has slightly better performance, though, if you want better multitasking and/or the resolution is reduced to the point of which fullscreen is a blurry mess, windowed may be a better choice.
MaxLights=1
More lights = more work. You need at least one light, so that's the bare minimum.
MapPreview=0
Map preview should be pretty lightweight, and it isn't seen in game, but could slightly improve performance.
To use these, open glestuser.ini in the MegaGlest data folder, and find the line specified and change the value accordingly. On a side note, I don't recommend using all the tweaks, but start with the most apparent, such as changing the resolution and disabling shadows, since some changes (such as disabling 3D textures) have hefty visual cons to offset the performance boost. Once you get playable gameplay, it'd be best to stop there, as you shouldn't be expecting 60 FPS on a netbook anyway.