Adding more ram

And here I said I wouldn't be asking any questions but this one is driving me mad

I have been trying to add more memory to my computer for the past year, I've bought 3 different sticks and can't get any to work

I have to 2- 512MB DDR333 sticks in it, one is Crucial and the other is Kingston, I'm trying to add another 512 of Crucial.

I was told that I need to change the settings of the ram via the bios but I'm unsure on how to change the ram settings in there

My system specs are http://us.dfi.com.tw/Product/xx_product_spec_details_r_us.jsp?PRODUCT_ID=2840&CATEGORY_TYPE=MB&SITE=NA

The manual tells me if all three sticks are DDR333 then you'll have to use the bios to down dimm 2 & 3 to DDR200 with dimm 1 set at 333

How exactly do I go about doing that?

 

All same type of RAM (DDR/Speed, not capacity) and all set at same speed, that is the bottomline. I have never seen anyone configuring each RAM stick to run at a different speed.
It doesn't make any sense since the mobo would utilize them at the slower end of the speed spectrum anyhow.