Squid Server – Voice & Video chat

I had configured a P-III 1.7 Ghz Machine with 256 MB RAM 40 GB HDD AGP display Adaptor on a Cyber cafe,with Linux Red Hat 7.0 as a Squid server and connected 12 clients machines with windows 98 OS Intel chipset Celeron standard machine,we are using one 8 port Switch and Hub with Zxyel TA for Internet Access, everything is working fine we are able to browse from every client what the problem is that we are not able to do voice and video chat…..plz suggest or guide me how to resolve ??