Eugene, you're not making yourself clear. The others have suggested you read the datasheet. I just went to the national website and had a look at the appnote for the chip you describe - they give a clear flowchart and assembler code - its not 'c' but its the concept that is the critical part.

http://www.national.com/an/AN/AN-280.pdf

Have you told us what 'c' compiler you're using?

Anyway... here's hint hint to get you started...
/*
shifts a byte out P1.0 MSB first using P1.1 as a clock

#define SCLK P1.1
#define SDOUT P1.0

void shift_byte(char val)
{
char bitcount,tmp;

tmp = val;
for(bitcount=0;bitcount<8;bitcount++)
{
if ((tmp & 0x80) !=0) //test most sig bit
{
SDOUT = 1; //clock a '1' bit
}
else
{
SDOUT = 0; //clock a '0' bit
}
SCLK = 1;
tmp<<=1; //shift the data along 1 bit
SCLK = 0;
}
}

This code shifts 8 bits out. You'll also need data in and cs port pins to control the a/d. The code to shift in the result is similar.

Please don't abbreviate 'you' into 'u'. Bad manners!