OK, option #2 - not as elegant, but something to try:
for each checkbox, give it a class ID, something like this:
<input type="checkbox" name="<%="InvoiceRun_" & rs.RecordID%>" class="chkbox">
This class ID doesn't have to be linked to anything, just a unique identifier for all checkboxes. This way, you can find & check all chekcboxes like this (VBScript, sorry!):
for each element in document.formname.elements
if element.classname="chkbox" then
element.checked = true
end if
next
This isn't elegant - it's actually rather ugly. It feels like more of a workaround than a solution, but it'll work. I'm sure there's a lot of better ways to do this though, so anyone else with ideas, go right ahead!
Hope this helps,
TBor