Km266-mnb Mother Board .... pc2100 ddr...

By this do you mean you want to increase the RAM on your computer?
I suggest you use PC2100 DDR RAM (same speed) and increase the total RAM to what your require but use the same RAM manufacturer if possible.
If you want to install more than 2Gb of RAM, check the motherboard specification for the maximum RAM that the motherboard can support.
Your motherboards may support more RAM with a BIOS upgrade.

no it wont here are the list that HD ram will work:
The following list comprises most of the motherboards stated to work with non-ECC High Density PC3200 memory. Though bear in mind that whether your particular board works with High Density RAM, and if it does, whether it will work with all slots filled with High Density RAM will always be something of a punt:
INTEL 915; NVIDIA NFORCE3 250GB; NVIDIA NFORCE4 SLI; SIS 645; SIS 648; SIS 648FX; SIS 650; SIS 650GX; SIS 655; SIS 661FX; SIS 746FX; ULI CHIPSETS; VIA K8T800; VIA KM333; VIA KM400; VIA KT266; VIA KT333; VIA KT333A; VIA KT400; VIA KT400A; VIA KT600; VIA KT880; VIA P4X266A; VIA PM800; VIA PT800; VIA PT880.
The following additional boards might possibly work with some High Density modules - but equally they might not:
SIS 649; SIS 651; SIS 656; SIS 661; SIS 748; SIS 750; SIS 755; SIS 756; VIA APOLLO P4X400; VIA K8M800; VIA K8M890; VIA K8N800; VIA K8N890; VIA K8T890; VIA K8T900; VIA P4M800 PRO; VIA P4M890; VIA P4M900; VIA PN800; VIA PT800; VIA PT890.
As a rule of thumb it seems safest to assume that no Asus or Intel boards (with the exception of the 915) will work with High Density RAM.