Yes you can run both i do ! Yea i found the poll button and clicked on it there are 2 boxes and alot of russian writing scared me =[
How to Run Quake 1.3 and 1.4:
1. Copy ur installation of Quake4 with 1.3
If u have installed quake4 with point release 1.3 in a path like this (for example)
"C:\Id software\quake4\"
..just copy ur whole quake4 folder to a folder named quake4old or wotever, so u will have
"C:\Id software\quake4\"
AND
"C:\Id software\quake4old\" .
2. Download the new version 1.4.2
Download the most recent version of quake4, its 1.4.2.
U may find it here:
http://www.idsoftware.com/
In the menu click on 1.4.2 Point Release and download it.
3. Install the new version 1.4.2
Now run the 1.4.2 point release and install it in ur current installation of quake4.
4. ALL DONE
U will be able to play old quake4 (1.3) when u execute ur quake from ur quake4old folder then and
U will be able to play new quake4 (1.4.2) when u execute ur quake from ur normal quake4 folder.
Have fun !