Unfortunately nothing good lasts forever. There are 3 routes you can go. Firstly you'll need to figure out if its a HD or DVD-Rom problem, clicking more thank likely is HD but my unit at times has problems and its the DVD-Rom not the HD.
1. Go on eBay and or some XBox mod sites and see if anyone is selling their original 8G HD there might even be some sites that sell replacement parts that sell that HD.
www.xbox-scene.com is a good place to start. If its the DVD there are links on the aforementioned site that will sell you replacement DVD drives for your xbox.
2. If its your HD time to mod your XBox with a larger HD. Many people tend to forget the other things you can do with a modded XBox, like host your mp3s, AVI and MPG files it can be turned into a multimedia server. Of course you can also find the emulators and play old school games like Joust etc.. on your modded XB.
3. Save your money and wait for the 360.
Ed