No gifts necessary. I love doing this stuff.
How to stay safe? Follow the recommendations I gave above and....

Watch what is downloaded , thoroughly investigate everything you download and don't take one rave review as gospel. If something claims to be the perfect "all for one" program...don't believe it.

Virtually everything infecting this computer was a Trojan or Trojan related;
Trojan horse is a program that installs malicious software while under the guise of doing something else. Though not limited in their payload, Trojan horses are more notorious for installing backdoor programs which allow unauthorized non permissible remote access to the victim's machine by unwanted parties - normally with malicious intentions. Unlike a computer virus, a Trojan horse does not propagate by inserting its code into other computer files. The term is derived from the classical myth of the Trojan Horse. Like the mythical Trojan Horse, the malicious code is hidden in a computer program or other computer file which may appear to be useful, interesting, or at the very least harmless to an unsuspecting user. When this computer program or file is executed by the unsuspecting user, the malicious code is also executed resulting in the set up or installation of the malicious Trojan horse program.
Also, download ONLY from a reputable site. That is not to say you cannot get a trojan from a reputable site but chances are slimmer.

Watch where you surf, don't have unnecessary IM programs running all the time, keep anti-virus, java, firewall and security programs updated, run anti-virus and security programs at the very least weekly, keep temp files cleaned up, no P2P stuff, that is a biggy in my book for causing infection...who is this nice person willing to "share" this $100 game with you for nothing....and WHY?