The motherboard is one of the most important part of your system. The motherboard more than anything else determines the stability of your system. I strongly advise against getting a cheap motherboard.
You seem to be looking for an Intel 845E microATX motherboard with good overclocking capabilities
Asus P4B533-M (Not a very good overclocker)
Jumper controlled FSB: 100/105/109/133/135/139/145
BIOS Controlled Memory 1:1, 3:4, 4:3
No voltage selection.
MSI MS-6507E
BIOS Controlled FSB (I don't know what range)
BIOS Controlled Memory Auto/DDR200/DDR266
No voltage selection.
You can go with the Intel 845G or Intel 845GL, but you will be paying for integrated graphics that you won't be using (since you asked for an AGP slot).
The EPoX EP-4G4M+ is an Intel 845G.
CPU clock settings are adjustable by BIOS in 1MHz increments.
Memory Frequency: Auto, FSB, or FSB*4/3
CPU V-core settings are adjustable by BIOS according to specs, but BIOS screenshots do not show this functionality.
AGP/PCI Clock: Auto AGP-FSB*2/3 PCI-FSB/3, AGP-66MHz PCI-33Mhz (Above 117MHz, fixed is forced)
So the EP-4G4M+ only supports a 1/3 PCI divider or fixed.
The EP-4G4M+ seems to be much more overclocking friendly.
Abit makes the BD7m (845 DDR). Abit generally makes at least decent overclocking motherboards. However, their appears to be little support on Abits web page for this motherboard and no manual for downloading. I will leave it at that to avoid the wrath of Abit fans on this forum, but I am no fan of Abit.
Gigabyte does not make any motherboards fitting your description.
Chaintech makes the 9EIL (845E), 9BIF (845G), 9LIF (845GL) and 9BID (845 DDR), but I do not recommend Chaintech (they do not make the most stable motherboards, their manuals are poor, and their support is virtually non-existent). I believe they do support BIOS FSB and Memory speed
configuration, but no voltage control.
Cheaper motherboards may not be voltage tweak-able and will have less flexibility with FSB changing.
Just to check, what do you mean by PCI/AGP Lock? Almost all motherboards use dividers to come up with the PCI/AGP bus speed (100/3 = 33, 133/4 = 33, 166/5 = 33). Are you looking for a motherboard that runs asynchronously with out dividers.
It definitely looks like meefmah is right on about the EP-4G4M+ being the best overclocking board.
[Edit: I would like to add the the 845 DDR boards listed do not support the 533 FSB P4.]
