Wow, Have you considered having an exorcism? lol, I'm just joking. While I Probably can't provide you with the fix to this problem, if you really are a mac newbie, than that means you probably don't have a lot of stuff on your mac right? My advice as a fellow mac newbie, (well, not really, but don't know enough aobut macs to offer any other help) Is to back up your data and reinstall from scratch.
By back up your data I mean to back up any data that you need to keep, by burning it to CD or DVD, by this I mean any documents you have created or saved on your mac, not any applications you have installed. Once you get that done, get out the Tiger DVD and put it in your mac.
Then shut down your mac,
Once it's shut down, turn it on while holding down the "C" key on your keyboard. (this will tell you mac to boot from the CD instead of the hard drive, just this one time)
When you see the Apple appear on the screen you you can let go of the "c" key.
Eventually you'll get to the installer, go through all the steps untill you get to the one where you see a picture of hard drive on screen, Then you should click on the "options" button.
Then choose "Erase and Install" This will clean off all the stuff you already have on your hard drive and give you a fresh install(like from the factory)
Continue the rest of the install process normally, when you get done you should have a fully functional machine.
If this isn't an urgent thing, or if erasing everything on your hard drive isn't an option for you, just be patient, I'm sure someone more knowledgeable than me will probably reply with another solution.
For future reference, you don't want to go and instal any program on your mac without first checking around to see about other peoples experiences with it.
Go to VersionTracker.com or MacUpdate.com and do a search for the program you are planning to instal, and read the reviews that other people have left for it.
I say again, don't just install anything without checking it out first. The main reason why the mac is so secure is that no malicous evil software can install itself without your permission. Whenever you install something, you know that screen that pops up and asks for your password? That's what I'm talking about. Once you give it permission it's gonna install itself and then you're gonna be stuck with it. (unless you can un-install it)
Also, Mac OS X needs a lot of memory, you have 512 installed so you should be ok. It also needs a lot of Virtual Memory, which is free space on your hard drive where it can stash stuff that it's working on behind the sences, so keep a couple of GB (that's gigabytes) of space free on your hard drive. To see how much space is free on your hard drive, select it (single click) and then press "Command" + "I" at the same time on your keyboard. You can also right-click, or Control + Click at the same time, and choose "Get Info.." from the pop up menu
Lastly, right now you don't need any Anti-Virus for the Mac. And (don't kill me for saying this anybody) it's not really because Mac OS X is more secure than windows (which it is) it's really because virus writers mainly target windows, because there is a lot more windows machines. They want the glory of crashing everybody's system, Mac users account for about 5% of computer users, so most virus writers ignore them, cause it won't create as big of an impact, no matter how l33t their skills are.
If you absolutely must use some anit-virus use
clamXav
there is a article on how to install it
here
I only recommend this because I've heard good things about it, such as that Apple ships it with the Server version of Mac OS X