said 12 months ago:
I see that the blog you have listed in your profile is using wordpress so I’ll assume that it’s the site you interested in using the “popup window” on.
Though I’m not a familiar with a particular wordpress plugin, the search terms you are looking for are:
wordpress overlay popup
Search Google or http://wordpress.org/extend/plugins/ and I’m sure you’ll find something.
On a personal note: I am not fond of these things either, but like you I have read countless posts and articles that say they are effective, and I believe they are.
So I think the question that you need to ask yourself is how do you want to be perceived by your audience.
An example would be a local acupuncturist using this on their hm page. As a potential client I’m not interested in a pushy acupuncturist who is trying to harvest my email when I land on his site to check them out. It’s just not the “energy” or personality that I’m looking for. Your business and site is a long way from this, but it seemed like an effective example to explain my point.