I did a quick check and verified that download.com actually is distributing Opera (http://download.cnet.com/Opera/3000-2356_4-10527779.html), but improperly naming it get.pl by default. The PL extension (versus DMG) prevents it from being recognized as a normal application, which is why it is being opened in TextWrangler, an application (advanced text editor) that is preinstalled on OS X. It is not dangerous in the least, and that download will work if you rename it, but I am reporting it so that it can be fixed to avoid future confusion.
I have a Mac OS X, Version 10.4.11 with Intel Core 2 Duo. (I'm more familiar with PCs.)
I have been using Firefox and Safari browsers. I tried to download Opera 9.64 from CNET, and it downloaded "get.pl". Not being sure what would come up, and trusting CNET, I went ahead and said "ok" when pop-up said this contained an application and did I want to download. I also "registered" during the download, thinking it was part of it. Now, I have TextWrangler, and when I click on "About TextWrangler", I get "TextWrangler, a product of Bare Bones Software, Inc., version 2.2.1 (186) of Wed, 14 Feb 2007, copyright