You will not be able to run all Athlons with a stock speed of 1400mhz, you should be safe with an Athlon B(200mhz FSB) with the L1 pins locked, if they are unlocked you can change the motherboards multipliers but due to how VIA designed the KT133 chipset this is not a possibility.
The KT133 chipset which indeed is a good chipset despite serious trouble with Creative sound cards, Live and Audigy series, offers very bad support for FSB(Front Side Bus) overclocking. Depending on the quality of your memory and other devices, NIC's(Network Interface Card), Video card(AGP or PCI connection does not mather since both are affected when the FSB is raised or lowered), I would be surprised it you could boot at anything higher then 115mhz(115*2=230mhz).
The next chip in the KT series, the KT133A has support for the Athlon C series which uses a FSB of 133(133*2=266mhz), both chipsets uses a DDR(Double Data Rate) FSB which effeciently works at a FSB of 200mhz(100mhz FSB) or 266mhz(133mhz), and has support for FSB speeds over 133mhz(266mhz). For the end user a higher FSB speed means better memory performance, the KT133A offers 17 % more effective memory handling compared to a KT133.
If you decide to use a locked, L1 pins unconnected, 1333mhz Ahtlon C processor your motherboard will recognize it as a 9*100mhz CPU, 900mhz, eventhough it's stock speed is 9*133mhz, 1333mhz. If you unlock it, by connecting the L1 bridges, you will be able to raise the FSB by a couple of mhz, 9*110mhz, 990mhz, but you will not be able to change the multiplier. Do not take my word for it, this could vary amongst motherboard and BIOS vendors.
Increasing the FSB to a higher level also means that you are changing the PCI and AGP speeds. The PCI divider on the KT133 is 1/3 which means that the PCI bus speed will be 33,33mhz(the speed it was designed to run at) when using a DDR or non DDR FSB of 100mhz. The AGP divider is 2/3 which means that if the FSB is 100mhz the AGP bus speed will be 66,66mhz(the speed it was designed to run at). And since the VIA KT133 chipset has support for AGP4x(4*66,66mhz=266mhz) alteration of the FSB, which affects the other busses, AGP, PCI, ISA, will cause an unstable system.
My advice to you would be to buy an locked, L1 pins unconnected, Ahtlon B(2*100mhz DDR FSB=200mhz) clocked at 1400mhz. And since your current processor consumes circus 40watts and an Ahtlon B clocked at 1400mhz probaly consumes 100watts, give or take 10watts you system will be unstable if your PSU(Power Supply Unit) can not provide you with enough watts. If your current PSU supplies you with 250w or more watts then you are safe but anything less, I am assuming that you have a atleast one HD and CD-ROM, could make your system unstable. Add a Geforce 2 Titanium 200 to your already stressed PSU and you are using it to it's fullest potential. The worst case senario is that your PSU is providing you with less wattage then all your components consumes, causing component malfuntion.
And before you go out and buy anything try to overclock your 650mhz Duron(6,5*100mhz DDR FSB=650mhz) and see at which level it fails to operate. The Duron 650mhz CPU default voltage is 1.6v, max voltage and AMD Duron and Athlon specification is 1.85v and it is very unlikely that your motherboard would support core voltage above the recomended max. If you are worried about frying your cpu because of the increased work load, set the voltage provided to the core to 1.75v, which is the default core voltage for the Athlon processor series. Read your motherboard manual for more instuctions, your motherboard should allow you to change FSB and multiplier by adjusting jumpers.
j64:
