Fire several onchange events in a row. One to set a session variable containing the record id you need to update, and a second event to actually do the record update. The example below does not do exactly what you want but you could easily adapt it to do so.
<tr style="font-family: arial; font-size: 10px; font-weight: normal; background: AliceBlue; ">
<td valign='top'><input id="hiddenClientId"
name="hiddenClientId"
value="[inccount]"
type="hidden"> [firstName] [lastName]</td>
<td valign='top'> <input id="hiddenClientName[inccount]"
name="hiddenClientname[inccount]"
value="[firstName] [lastName]"
type="hidden"> <input name = 'newHours[inccount]'
id = 'newHours[inccount]'
value='5.5'
type='text'
size='5'
onchange="checkhours(this.value,'newHours[inccount]');"
disabled=true>