Código PHP:
<tr>
<td valign="top" bgcolor="#FF9900" class="Estilo12"> </td>
<td class="Estilo12"> </td>
<td class="Estilo12"><div align="center">
<input name="caballo[1]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="caballo[2]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="caballo[3]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[4]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[5]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[6]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[7]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[8]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[9]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[10]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[11]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[12]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[13]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="carrera1[14]" type="checkbox" onClick="Suma(this.checked,this.value)" value="1">
</div></td>
<td><div align="center">
<input name="total" type="text" value="0" size="20">
</div></td>
</tr>
De verdad se los agrdezco.