If you only have HTML available then I would use javascript, there's an activex object that allows you to read a file, though I've never used this. The trouble is it sounds like what you want to do is something that would usually need to be done server side, and it would be a piece of piss to do via php or .net.
A javascript example would be (and this is totally googled, I take no credit):
Code:
<script type="text/javascript">
var activeXO = new ActiveXObject("Scripting.FileSystemObject");
var f = activeXO.OpenTextFile("c:/testing123.txt", 1);
alert(f.ReadAll());
</script>
If you were to use php there's a whole series of commands for controlling files.
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