Okay, yeah. I did some more research, and Nulware is definitely spyware/malware. What you need to do is, first of all, get a good anti-spyware program like Ad-Aware or Spybot if you don't already have one. If these programs aren't picking it up, you need to manually search for and delete any occurrence of "nulware.exe". Also, you will have to open your registry editor and delete all instances of "nulware" (make sure you back up your registry first!).
It seems that Nulware might be linked to the Search Assistant spyware, but not necessarily. In any case, your anti-spyware program should at least pick that up. Good luck!