Without Javascript? Well, I'd probably go with something like waswas-fng's suggestion, but the only non-JS solution I can think of (no, VBScript is not a solution to anything :o) is:

<form action="scr_res.pl" method="POST">
 Please enter your screen resolution:<br />
 Width (px): <input type="text" name="res_x" />
 Height (px): <input type="text" name="res_y" /><br />
 <input type="submit" value="Submit" />
</form>
[download]

LAI
:eof