If your XBOX360 is giving errors reading disks or crashing when games are loading then you may be able to repair it yourself using the pot teak method. Team Xcuter have an excellent write up on adjusting the pots on your DVD drive. I would highly recommend that you buy a case opening tool, they are easy to find online with ebay being a great source. Most come as a kit with an allen key that fits the screws on the case.
You will also need a multi-meter as recommended in the article and a small flat head screwdriver to adjust the pot. http://team-xecuter.com/forums/showthread.php/61768-Disc-Read-problems-How-to-POT-Tweak-Xbox-360-DVD-Laser
Eventually the laser does burn out and you will start having disk read errors again. All is not lost though as lasers are easily available online.
I purchased mine from ebay although there appears to be some debate over the quality. I purchased mine from a seller with good feedback and it works very well. To replace the laser you need to open the XBOX360 again and remove the DVD drive. The DVD drive itself the needs to be disassembled and the laser removed. It is a fiddly job but it is not difficult. One point to not is new lasers have a short in their circuit to protect them from static. This needs to be removed before the laser will work. You will need a soldering iron and desoldering pump for this.
There are two good guides on opening the XBOX and the drive here