I gave you this info by PM as well, but as it may be handy to others, I'll repost it:
I have installed this add/on 2 times. The first time something went wrong, I broke my vbulletin and my site was down for some time. I did find a solution for this, that works very quick, easy and safe:
1. If you are not on vbulletin 3.6.8, then upgrade now.
2. Edit the .php files according to the instructions in prefixinstall.php
3. Upload the .php files
4. Install the
Template Modification System ( easy to do and you'll be very happy with it)
5. Instead of going using the thread prefix its 'prefixinstall.php' further than step 1, use the Template Modification System instead: simply upload the templateedits-threadprefix.xml that you will find in the demo folder of the Template Modification System's zip.
That's it. Instead of 30 minutes installation time, you will now have it installed in 30 seconds. (not counting the short installation of the TMS)