I personally doubt that the motherboard was made specifically for that pc, it may just be a smaller form factor mobo (not atx). It may be possible to recoup some of that speed if the bios allows you to raise the fsb either through a preset(i.e. 133, 166, or 200, but not likely since its sold as 533 and thats prolly all its got) or by incremental fsb adjustments. But its highly unlikely that youll be able to raise it 77mhz to make up for the speed loss. You have two options from what I can see:
1. Return the CPU and get one thats made for 133 bus. Youll be better off because the CPU will have a higher multiplier than the one you currently have and will thus run faster.
2. Measure the motherboard to find out what form factor, if any, it is. If it turns out to be a standard size board. See if you can get one that'll support that 200 mhz bus. Keep in mind though that if you have already bought some slower RAM youll need to upgrade that as well.