No, I was clarifying, because he could've meant the rated speed was 333Mhz (ie. 166Mhz base clock), which is DDR1 PC2700 RAM.
And having a Celeron CPU, it's not at all uncommon to have DDR1 RAM...

Checking the Biostar website, apparently your board only supports DDR2 400/533Mhz RAM

well thats ok dunno the difference between ddr2 and ddr3 ram,its that faster or it isnt any noticeable differenence

Yes, it's faster, and DDR4 is faster than DDR3 and DDR5 is faster than DDR4, and so on (currently DDR4 and DDR5 are only available on graphics cards).
DDR3 starts at 1066Mhz, whereas generally DDR2 only goes up to 1066Mhz (though there are a few 1200Mhz models available).
Upgrading from DDR2 to DDR3 RAM with a Core 2 Duo CPU won't yield any significant performance increase either, and will require a new motherboard as well.

usually but not always, there are boards like asusp5kc which supports both types

I wouldn't trust those combo boards. They often have stability issues using either types of RAM. And there really is no point in getting a combo board, since you can't use both at the same time anyway, so if you plan on using DDR3, then you should just buy a dedicated DDR3 board. If you have DDR2 RAM, chances are that you already have a DDR2 motherboard (who gets RAM without having a motherboard?) and have no reason to switch.

NOt quite. Lets say you buy such mobo with pentium dual core like e5300 with 800hmz ddr2 ram. Some time later you want upgrade it a little bit to e8400 or quad and OC it, 800mhz will not allow OC of such CPU. DDR3 would be quite usefull here ... Of course if board cant have ddr3 you can always buy high quality 1066 ddr2 to give some not bad results but ddr3 1333mz would be nice for that.

But the combo boards have had stability issues, especially at high frequencies, so I wouldn't trust them. They are also quite a bit more expensive than regular boards and they only have 2 DDR3 slots.

Any Core 2 Duo won't need more than 1066Mhz RAM for overclocking (on air anyway). This is of course assuming you overclock the RAM as well if for some reason you reach 533Mhz FSB. Most 800Mhz RAM will overclock to around 900-950Mhz as well, and that is also sufficient up to 450-475Mhz FSB. Clearly there's no need for DDR3 unless you go into LN2 1.8+v territory.

Besides the fact you can just decrease the RAM multiplier..

decreasing ram multiplier with 800 mhz ram and 1333mhz cpu is barely possible since its automaticaly decreased almost to minimum (5:6) to reach stock speed.

The whole ratio thing doesn't make much of a difference, it used to, but not now..

Then again, I'm not much of an Intel user.