Hmm, could be a trojan agent, or the remains of one. See here: <a class="postlink" href="http://greatis.com/blog/how-to-remove-malware/rundll32-dll.htm" onclick="window.open(this.href);return false;">http://greatis.com/blog/how-to-remove-m ... 32-dll.htm</a>.
Go to start>run and type in msconfig. Go to the 'startup' tab. Have a look for anything that is listed on there that shouldn't be, and uncheck it. Alternatively, use CCleaner, as suggested, and go to tools>startup, and disable it from there. Probably best to run a virus scan, but I'm assuming you do that anyway. Worth downloading the free version of Malwrebytes Anti-malware, and giving that a run too. Do a registry clean afterwards.