Someone's website is using part of my trademarked name, is there anything I can do?

The only way to determine if one trademark is confusingly similar to another -- or whether a domain name unfairly includes another's trademark -- is to evaluate the trademark and the domain name. No one can answer your question, therefore, without knowing what you use as a trademark (and the precise services you offer under that mark) and the domain name that the other person registered.

I caution you against providing that information in a public forum such as this one and suggest that you call a trademark attorney in your state. Some attorneys will provide a free consultation. You could also contact a local law school that has a legal clinic or a friendly intellectual property professor who may discuss your . Good luck.

Unfortunately, such a specific question simply cannot be answered in a forum like this, you will really need to speak with an attorney to decide on the best course of action.
There are a number of factors that will determine your likelihood of succeeding in a trademark dispute. Ultimately, the issue is how likely is it that someone will confuse your business with the MLM business. Exactly how the likelihood of confusion is determined will depend on whether yours is a state (and if so, what state?) or federal trademark. The portion "Judging the likelihood of confusion" from the below linked Wikipedia article will give you some background on what a court would probably look at in determining if your mark is being infringed.