Are you at risk? Sure, we all are. I have no idea what defenses you have on your system. Do you have a firewall? Do you have an antivirus program? Do you have filesharing on? You get my drift, so I won't continue.

Just do some cursory searches on firewalls, etc to see what you can do. I'm curious as to what you did to change your IP. Are you on dialup or do you have multiple ISPs? Somebody will always be able to get your IP, so I would focus on protecting your computer, not your IP.