where IS the metal greymon in bios domain? or can you only get him the first time you enter bios domain?

I think you can find him on the boss floor. And as long as you dont beat him or catch him he will be there until you do one of the two.

Cool thanks. i don't really intend to use him, but i need a strong digimon to DNA with my Exveemon to get a veemon. That or he'll DNA with megadramon. What should I do with it?

Its really up to you. I dna him with megadramon and you get greymon but he can go all the way to wargreymon who is very powerful. But like i said its your choice.

i can't find him anywhere, and i've been to every room on every floor.what am i doing wrong??

Well, if you don't fight him the first time your in BIOS domain, you can't find him there anymore. If I remember right, Akira says that "MetalGraymon must be long gone by now."

how can u get metalgreymon (from bios domain) to join ur team?(like using 2toyairplanes?)

When in the same room as him, press the Square button, then press X, and then select a gift to toss at him (like a Toy Plane) and press X again. That is assuming your Shooter Gun is not damaged. Throw him gifts that he accepts (i.e. gifts of the same type as him or gifts that work on all Digimon types) until a heart appears above him. When that happens, you have a chance of catching him after defeating him. The bigger the heart, the greater the chance. Also remember that to catch MetalGreymon, you must also have space for him in your Digi-Beetle's Memory.