I wrote a small tutorial for converting subtitles into other formats without installing any type of software in our machine.
I will be using SubtitleSync (http://www.subtitlesync.com.ar/), which supports 19 differents formats (such as SRT, SUB, SSA..)

Step 1. First, go to http://www.subtitlesync.com.ar/lang-en/subir-subtitulos.html



Step 2. Upload the subtitle you want to convert by selecting the sub and pressing Upload.
When the file is successfully uploaded, a list of options will appear below the upload form



Step 3. Press the Convert button. A popup window will appear. select the desired format from the combo box (SubRip (.srt) is most likely the most supported format). Press Accept.



And that's it. A new dialog will be shown to download the converted file.

I hope this tutorial is useful.
Bye