I found it! Well, I'm pretty sure this is the right one. If it is, it'll go through the whole abduction scenario and everything. When I had been using it, I was trying to get an old man alien pregnant... then realized the game considered him too old for childbirth. o_0 Still, it would go through the whole scene each time and by the fifth failed implantation attempt, he got REALLY obsessed with meeting his alien "friends."

Yeah...

Anyway...

Here's the download link: http://www.sendspace.com/file/ktmc0l

The bit from the site I got it from says:

Tired of not getting your sims abducted? Well now there is a solution! Download and extract this file into your My documents\EA Games\The Sims 2\Downloads and you can get abducted every night between 7pm and 2am whenever you stargaze with the expensive Telescope (which is replaced using this hack, so if you have it on your lot you don't need a new one). After you get as many abductions as you want you can simply delete the telescopehack.package from the downloads folder and everything will return to normal. All I did was change the behavior to ignore wether or not the random number was correct for abduction, so it shouldn't cause any problems. Have fun with those green babies!

I got it from Modthesims2.com You have to register to download stuff, but its free. They have all kinds of mods, stuff like this: http://www.modthesims2.com/showthread.php?t=145882