Can I get viruses/trojans/bad things from chat programs?
You sure can. Worse, AIM itself is fairly hackable. To keep your computer secure, I recommend using Trillian or Pidgin for chat instead of AIM. They are much better organized, have nicer features, and both connect to your buddy list the same way AIM does. Best of all, they can connect to several different chat clients at once–that means you can fire up Trillian and talk to your AIM, MSN, Yahoo! and IRC buddies all in one program.