well, if you still have the original cd then you CAN get a backup or what not. Technically, you are NOT purchasing the CD and software, you are purchasing the rights to use it. Here is one example:
he Microsoft EULA requires that the same CD that was distributed with the COA be used to reinstall it. However, any XP CD of the same type may be used. An OEM CD for and OEM Product Key, a retail CD for a retail key, etc. Chances are these computers were preloaded from the factory and you need an OEM cd. Upgrade CD's cannot be used for a full reinstall. (Unless of course you installed Windows 98 first and then upgraded with a valid upgrade key).
So, you may wanna google this as there is some info you need to look into first. If you doubt that you can copy a CD (and depending on what kind and where you go the system, you MAY have to have the original cd to copy it legally, or you may not) you CAN copy your cd. Hell, microsoft even explains slipstreaming service packs, thus telling us how to create our own custom bootable installation cd's!