Please help me! My computer's a mess!

Okay, I'm in a bad spot. I'm not dumb with computers, but I'm not saavy by any means. Anyways, I believe my computer's been hijacked. I was booted off the computer and when it reboot (and since then), I haven't been able to access the internet. An "anti-spyware2009XP" program autoloads (which seems as though it wants to help, however, I believe it's the cause of my problems). There's a "Windows Security" icon in the system tray (which doesn't look like the normal one) that keeps opening a balloon telling me that "my computer is infected" and that I need to run the afore-mentioned program to get it cleaned. But it never goes away. Since then, I haven't been able to access any "http://" websites. It lets me go to "https://" websites with no problem. And that balloon that keeps coming up is annoying as heck! I was able to open an old Ad-ware program I had and it said I had 41 files at risk and I cleaned/quarantined them, but this did not help. Of course, it hasn't been updated in 2 years, but the link to update the program ends in an error (because, I'm guessing, the lack of whatever it is that's not letting me connect to the internet properly).

Needless to say, I'm at odd's end and I need some help. Anyone that can get me on the right track, I'd be overly grateful to you!

Oh, by the way, I logged in under a second user on my computer and I still have the same issues as above, however, (and strangely enough), I'm able to access "some" regular "http://" sites like this one. Some others have failed with the same error message. I'm just thankful that this link works in hopes that I get a response and on my way to getting my computer healthy once again!

Thanks in advance for anyone willing to help!