In draw.h under 
void Draw_String (int x, int y, char *str);
Add
void Draw_Crosshair(void);

In view.c near top in below

cvar_t	crosshair = {"crosshair", "0", true};

add

cvar_t	crosshaircolor = {"crosshaircolor", "79", true};

at the bottom below

	Cvar_RegisterVariable (&crosshair);

add
	Cvar_RegisterVariable (&crosshaircolor);


For glquake:
In gl_draw.c

among the variable declartions at the top (under int char_texture for example)
add

int			cs_texture;
static byte cs_data[64] = {
	0xff, 0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0xff,
	0xfe, 0xff, 0xfe, 0xff, 0xfe, 0xff, 0xfe, 0xff,
	0xff, 0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xfe, 0xff, 0xff, 0xff, 0xff,
	0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff
};

extern cvar_t crosshair, cl_crossx, cl_crossy, crosshaircolor;

Note:0xfe=a pixel, 0xff = no pixel, so u can edit the x-hair here.

find the Draw_Init function, below the line

char_texture = GL_LoadTexture ("charset", 128, 128, draw_chars, false, true);

add

cs_texture = GL_LoadTexture ("crosshair", 8, 8, cs_data, false, true);

Now add this function below the Draw_debugchar function:

void Draw_Crosshair(void)
{
	int x, y;
	extern vrect_t		scr_vrect;
	unsigned char *pColor;

	if (crosshair.value == 2) {
		x = scr_vrect.x + scr_vrect.width/2 + 1  + cl_crossx.value; 
		y = scr_vrect.y + scr_vrect.height/2  + cl_crossy.value;

		glTexEnvf ( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE );
		pColor = (unsigned char *) &d_8to24table[(byte) crosshaircolor.value];
		glColor4ubv ( pColor );
		GL_Bind (cs_texture);

		glBegin (GL_QUADS);
		glTexCoord2f (0, 0);
		glVertex2f (x - 4, y - 4);
		glTexCoord2f (1, 0);
		glVertex2f (x+12, y-4);
		glTexCoord2f (1, 1);
		glVertex2f (x+12, y+12);
		glTexCoord2f (0, 1);
		glVertex2f (x - 4, y+12);
		glEnd ();
		
		glTexEnvf ( GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_REPLACE );
	} else if (crosshair.value)
		//Draw_Character (scr_vrect.x + scr_vrect.width/2-4 + cl_crossx.value, scr_vrect.y + scr_vrect.height/2-4 + cl_crossy.value, '+');
	Draw_Character (scr_vrect.x + scr_vrect.width/2 + cl_crossx.value, scr_vrect.y + scr_vrect.height/2 + cl_crossy.value, '+');
}


Now open gl_screen.c

Right at the bottom find 

if (crosshair.value)
	Draw_Character (scr_vrect.x + scr_vrect.width/2, scr_vrect.y + scr_vrect.height/2, '+');

Comment out Draw_character call, and put Draw_Crosshair instead so it looks like this:

if (crosshair.value)
	Draw_Crosshair();
	//Draw_Character (scr_vrect.x + scr_vrect.width/2, scr_vrect.y + scr_vrect.height/2, '+');

Thats it for GL. 

For software rendering open draw.c

Under the Draw_String function add these functions

void Draw_Pixel(int x, int y, byte color)
{
	byte			*dest;
	unsigned short	*pusdest;

	if (r_pixbytes == 1)
	{
		dest = vid.conbuffer + y*vid.conrowbytes + x;
		*dest = color;
	}
	else
	{
	// FIXME: pre-expand to native format?
		pusdest = (unsigned short *)
				((byte *)vid.conbuffer + y*vid.conrowbytes + (x<<1));
		*pusdest = d_8to16table[color];
	}
}

//Erm yuck, should be ok once u cut and paste it tho

void Draw_Crosshair(void)
{
	int x, y;
	extern cvar_t crosshair, cl_crossx, cl_crossy, crosshaircolor;
	extern vrect_t		scr_vrect;
	byte c = (byte)crosshaircolor.value;

	if (crosshair.value == 2) {
		x = scr_vrect.x + scr_vrect.width/2 + cl_crossx.value; 
		y = scr_vrect.y + scr_vrect.height/2 + cl_crossy.value;
		Draw_Pixel(x - 1, y, c);
		Draw_Pixel(x - 3, y, c);
		Draw_Pixel(x + 1, y, c);
		Draw_Pixel(x + 3, y, c);
		Draw_Pixel(x, y - 1, c);
		Draw_Pixel(x, y - 3, c);
		Draw_Pixel(x, y + 1, c);
		Draw_Pixel(x, y + 3, c);
	} else if (crosshair.value)
		Draw_Character (
			scr_vrect.x + scr_vrect.width/2 + cl_crossx.value, 
			scr_vrect.y + scr_vrect.height/2 + cl_crossy.value, 
			'+');
}


Open view.c again, find this bit (near bottom)

#ifndef GLQUAKE
	if (crosshair.value)
		Draw_Character (scr_vrect.x + scr_vrect.width/2 + cl_crossx.value, 
			scr_vrect.y + scr_vrect.height/2 + cl_crossy.value, '+');
#endif

Comment out Draw_Character, and put Draw_Crosshair in instead so it looks like :

#ifndef GLQUAKE
	if (crosshair.value)
		Draw_Crosshair();
		//Draw_Character (scr_vrect.x + scr_vrect.width/2 + cl_crossx.value, 
			scr_vrect.y + scr_vrect.height/2 + cl_crossy.value, '+');
#endif


Carefull if u cut and paste my code, u may need to add some extra comments (//) due  to me writing this in notepad :)