Why did my hardrive get wiped clean when I did a simple system update?

On May 4th, 2010 my eMac, which is running Mac OS X (10.4.11) did it's automatic system update. I bought this eMac it was a refurb from eBay. I never had a single problem, it ran perfectly fine when I had tested it out, everything was great. I transferred some photos and music from my old Windows computer to the "new" eMac, and some of the music was newer and needed a system update to work properly. I thought nothing of it so I went to www.apple.com and looked for the update, found it, and started it. I had went ahead and stepped away while it updated to pass the time. Once I had gotten back I went ahead and restarted the computer like you must do with every update, when I had logged back in, my hard drive was wiped clean. At the time I was a little perturbed to say the least, but I passed it off as it not having an update in so long that it had just, more or less, reinstalled the new system update. Once again I passed it off not thinking anything of it, never had another problem out of it at all. I had put a many of programs such as Adobe Photoshop CS3, Adobe Audition, Dreamweaber, Garageband (full version), djay v3, and I had even JUST put Logic Studio on it, and many others. After putting, more or less, my entire livelihood on the eMac, (I create website designs, various ads, freelance photography and videography, and a verity of other logos, designs, insignia, emblems, ect...) it did another automatic update, now my ENTIRE hard drive is wiped clean. I no longer have possession of my software discs due to someone stealing them along with all my audio cds, and dvds. I don't have the money to spend on new software, (altogether my software added up to just over $2.5k) and now I am already feeling the effects. What can I do? Will Apple even help?

As for your comment on this being my first Mac, and the program issue, you misunderstood. Yes the eMac is in fact my first, personally owned, Mac computer other than the original Apple II series floppy fed PC, in which me and my father owned. The only other Apple/Macintosh computer I had experience on was my father's 13" MacBook Pro, and 20" iMac (both ran OSX Tiger 10.4.11, just as the one I have know runs). The iMac was upgraded to Snow Leopard due to our need for better picture/video/audio editing software such as that of Adobe, and the Macbook Pro was sold because of a business that was started being siphoned out of money. I purchased the eMac from a small business based off of eBay. It had the majority of OSX Tiger software, only missing minor programs like Photobooth. Other than that, it had no wireless software like BlueTooth, Wi-Fi capabilities, wireless sync, ect... But alas, when you buy a Apple/Mac computer, you must take a few cutbacks when purchasing it (even refurb.) for around $120.00 including taxing, shipping, handling, ect... I purchased nearly all of my software from co-workers and friends who had an extra key, or I would receive the software disc from them, and buy a key. The only "illegal" thing I had on the computer was music I had downloaded from LimeWire. I have never, and will never, trust any software coming from a torrent download site.