Don't know about a utility, but many ISP's allow free dialup for their cable modem/dsl customers. Earthlink for instance does this. You could check with your isp and see if they provide this service as well. You could then dial up and give it a try without having to actually pay any money.
Another more tricky thing is that many cable/dsl modems allow you to adjust their bandwidth, upstream and down. Some people use this to unthrottle their modems, but it's a risky proposition as many isp can detect when this occurs. Don't know if they'd complain about you setting your parameters to _lower_ than what your account calls for though. I recommend a google search if you're interested in this route.