First things first. You could have prevented this with any of the decent anti-virus apps out there. I personally use AVG Internet Security. Yes it costs $55 per year, but it keeps everything clean and happy. They have a free version, but it does not protect against downloads. You have to have the paid version for that.
Now as far as cleaning the dirty drive, here is what I do (I do this for a living):
1) Download the newest AVIRA AntiVir Rescue System
HERE. I would get the EXE version since it has a built in burning app. All you need is a CD burner and a blank disc. Burn the CD. Leave the CD in the drive when finished.
2) Download and install HijackThis
HERE. Reboot.
3) Boot from the AVIRA CD and follow the steps and choose to rename all infected files. It will simply add an .XXX extension to any infected file. Remove the CD and reboot.
4) Boot to SAFE MODE and search and delete every file that ends in .XXX.
5) Run HijackThis and do a system scan only. Look through the list of results for anything that looks fishy. This is where experience comes in. I know what to look for, but you may not. If you are unsure, better be safe and not remove it. If you can identify anything in that list, leave it be. If it looks odd, it probably should not be there. Check the bad results and hit Fix Checked. Reboot.
6) Now back in normal mode, see if the balloon still appears. All
should be clear now. If not, go back to step 1. You missed something.
7) If all seems good, I recommend buying the full version AVG Internet Security
HERE. That is up to you. I have tried most of the free versions of AV's and most are lacking in some respects.
Hope that helps. I do this on about 5-6 PCs per week and have always found it is very effective against almost every single malware I have come across.
BTW, people pay me $100 per instance to do the above.