Eww... eval(). That's about as bad a smell in JavaScript as it is in PHP.
But anyhow; I don't know what browser you're using to test this in, but in mine when you hover over a link the status bar shows the URL. In this case it's javascript: popUp(, because then the ' ends the attribute.
Use " for either the quotes around "javascript: popUp('detail.php')" or around "detail.php". While you're about it, consider also using quotes around your other HTML attribute values, too. Consider using CSS to do styling like text alignment, background colour, and font weight (you have an id attribute there: use it - unless you're using an id of "title" more than once on the page, in which case that needs to be fixed, too).
Oh, and unless you really do want to plonk those JavaScript variables out there in the global namespace (it looks like you meant them to be only local variables), you mean "var day" and "var id". Do you ever actually use "pageid" for anything? I doubt it, because if you did you'd use a variable name you'd be able to remember long enough to use again later. If you don't, there's no point declaring it, and there's no point in using eval() (in fact, there's almost never any reason to use eval()).
Incidentally, you don't need toolbar=0, location=0, statusbar=0, menubar=0, or resizable=0. They default to 0 anyway.
