not really, it is not required to turn firewall completely off to allow video connection to get thru. You can have firewall turned on but open ports required for HOVRS or Hamilton. In my case, I am mac user and I use iChat in Mac os X. I already have created setting in firewall to allow videochat to get thru bidirectionally. It does not slow down or choppy.
Keep in mind, I don't use router. If using router just enable firewall in PC. XP comes with firewall software built in. It will notify you that certain software is trying to get thru while attempting to use videochat then you can click "ok" to open the port.
for HOVRS, take a look at those FAQ;
https://secure.hovrs.com/cc/faq.aspx
You still can have secure connection with certains ports open required for HOVRS video chatting.
as for AIM videochat this page will tell you which port to open;
http://aimtoday.aim.com/features/main_redesign.adp?fid=video_im