I've been given a 256k modem for a 2 day event to allow users access to the internet. There will be multiple connections (I anticipate 30+). How can I set this up so that it can support that many connections at once or what are some other ways to get around this problem?
Here are some some vague hand-wavy remarks.
If you want more detailed responses, we need more detailed information (see my comment in the OP).
This is doable, but it depends on many factors, I've hosted 60-100 users on 512kbps with a 1000ms+ delay. It wasn't pretty but we were able to accomplish work.
I would consider using a firewall/router with a caching proxy. We use pfSense as our firewall of choice and it has package for squid proxy. It allows for doing transparent caching of HTTP. You can also use pfSense's traffic shaping to prioritize certain users or types of traffic.