Kaelynn,
if it is a branded name notebook you can normally go back to the manufacturer and purchase a recovery cd or a hot load cd, the cost of this varies for each manufacturer, these cd's have all the standard software, operating system and device drivers for your notebook so you can reload it back to the way it came if it was brand new.
you can also belive it or not ring up microsoft and tell the you lost your cd and for $25 they will send you another one.
if you are going to get an operating system (xp) cd from someone else then you need to make sure its the same version as the one you have now or the key want work to install it (ie you can not use a xp home cd if your notebook has xp pro installed), you should also check you have a valid key, on most notebooks if you turn them over there should be a sticker on the back that has a key and what version windows the key is for.
there are several things that can make you notebook or pc slow and they could be (1.) lack of ram, ie microsoft state that the min ram for xp is 128mb but trust me it works much better with 512mb. (2.) you could be runingout of hard disk space so you would need to check you plenty left. (3.) you could have spyware or a virus loading at startup that could be using all the resorces and thus making the notebook run slow.
so to check this do the following 1 click start, then run, type msconfig, click ok, a screen wil come up called system configuration utility, change the startup selection to diagnostic, click ok, the computer will now ask you to restart so say yes.
when the computer restarts it should be running faster as nothing is now loaded, so open your web browser and go to this address
http://www.trendmicro.com/en/home/global/personal.htm
on the right hand side you will see an icon that says "free housecall" click on this icon, click on the icon to the left of "scan my pc", select the countryand click go, click on the red magnifing glass, and select full scan, this will scan for virus's and spyware for free and is excellent, select only you hard drives
and click next, now just follow the prompts and if it finds any thing tell it to delete or fix it.
once this is completed restart the notebook, click start, click run, type msconfig (if its not already there) click ok, select normal startup, click ok and let the notebook restart.
if trend found any thing and removed it the notebook should be running faster now, if not you will need to look at the ram or hard disk.
I hope this help