That (2000) should be sufficient z-index to overdome the slide show's (it uses a top z-index of 1001).
However, it (the pop up) must be position either absolute or relative (fixed position will work too, but not in IE 6 and less).
Not only that, if the pop up has parent elements with any of these position values (fixed, absolute, or relative), then these must also have a higher z-index than the slide shows.
And if the slide shows have a parent with those position values, then their z-index must be lower than the pop up's and its positioned parents (if any).
There's always the posibility that something else may be causing this.
If you want more help:
Please post a link to a page on your site that contains the problematic code so we can check it out.
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