Use a single stylesheet, keep it small, 8 kB or less. Use no images for page layout unless absolutely necessary.
Read Brett's advice, 26 steps, reread the page size advice, follow it.
Test it on a dialup modem, make sure to clear your browser cache each time you check the load speeds. Aim for first view load times of 5-8 seconds, for all of it. That's not that hard. Once css is cached, along with any necessary layout images [use the same ones for the whole site if you have to use images for layout, so they can get cached] aim for page loads of 1-3 seconds, not hard if templated html is clean, full css.
Internet connection speeds in the 'developing' world should be assumed to be very slow, I read once that I think uganda had somewhere around the total bandwidth of I think a single high end cable connection here. Might have changed since then of course.
I'd target a decent user experience at 33 kb per second connection speed, that's not very difficult to achieve if you reject any and all eye candy from your design.
But it can still look very pro and clean without all that junk.
Above all though, NEVER use images for navigation, especially mouseover type images, total waste.