Disabling IE keeping e-mail?

I have my LAN with a NT4 PDC (soon to migrate to W2kServer) connected to a Cisco router that acts as the gateway for outbound internet communications. My problem is that I have limited bandwidth (ISDN) and want to disable the use of IE but not of e-mail for some users. How do I accomplish that without having to tamper with router settings and not having a proxy?