My suggestion is to wake up and smell the coffee. The closest you'll come to that is the MSI 865GM2-L (something like that) motherboard. Newegg sells them for just under $90. It is mATX and (as the model name implies) uses the 865G chipset with integrated video, AGP8X slot, 800MHz FSB, HT support. If you read the buyer's comments on the board at Newegg, you'll see that Vcore settings didn't "stick" meaning they can set them in BIOS but voltage didn't change. Newer BIOS removed the setting for Vcore.
I got one of those boards and indeed no Vcore, though there was FSB settings in 1MHz increments and even an AGP/PCI lock. I used a P4 2.6C chip that had been running stable for almost a year at a mild overclock of 2.84GHz and a pair of Kingston HyperX PC4000 512MB. Runs great at default. Don't want to overclock, sometimes hanging at POST or not even POSTing.
If you don't have to have mATX, then any of the budget ATX 865PE chipset boards from MSI, Abit, etc. would fit your needs. Otherwise, a very expensive option would be to get a Shuttle XPC. Those use 2 slot (1 AGP, 1 PCI) flex ATX motherboards. Smaller and more expensive, but some of the higher end models do have verified working overclocking features.
Summary is that you can have two of the following:
OVERCLOCKING + SMALL SIZE + BUDGET
If anyone can find and verify a motherboard that fits all three, I'd LOVE to know.