If you mean you have a 128MegaBYTE and a 256MegaBYTE SDRAM (or DDR SDRAM) DIMM, then yes it should run fine. If the mobo supports dual-channel memory you won't get dual channel (but you won't get dual channel with 1 stick anyways), but it should work fine.
If you really mean you have a 128bit chip and a 256bit chip, then no, they won't work because the socket on one of them won't fit.
If neither of the above is true, then I'm confused. :?
Ok, I think you're talking about the actual chip in the DIMM instead of its interface to the PC. I don't know much about that in detail (hence my earlier confusion), but AFAIK that depends on the mobo whether or not it will work. If the mobo can handle the higher matrix, then both should work fine. If the mobo can't handle it, then it won't work. You'll have to check the mobo mfg.
I checked and it doesn't say. It says everything else but that. Would the memory controller have that type of information. I remember there would be a software that could tell me whether my ram is a 128 bit or 256 bit.