Yea i have vista 64 bit also and had problems so get the 32 bit thats the sweet part of 64 bit system you can run 32 bit on it anytime and yea you can try right click and run it as a admin
1) got to C:\Program Files (x86)\Ventrilo
2) right click the vent launcher
3) click properties at the bottom
4) click on compatibility tab at the top
5) check the run as administrator box
6) if that fails repeat set 1-4 and click on the box at the top that say run this run this compatibility mode and select window xp sp2
If i where you i would just remove all of vent and re download the 32 bit version even thought you already tried it you said