Which Operating system? I am pretty sure you can order a replacement set from Dell themselves. You could try their support site and then put in your computers serial number. If you registered the computer when you bought it you won`t have to do this, then e-mail support and tell them the problem. There will probably be a charge but someone here may be prepared to send you a copy of the disks.
I strongly recommend you download Belarc click here run it and print out the results. This will give you all the current info about your computer including software registration keys. If you do suffer a crash and have to reinstall all the keys will be recorded in case you can`t find original disks.
I would also recommend you download all the updated drivers for your Dell and burn them to disk. Then you are prepared for the worst scenario. click here